typescript demo step by step

01_simple/Readme.md

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+Для того что бы увидеть как typescript подсветит ошибку необходимо выполнить шаги:
+
+1. Установка
+
+```shell
+npm install -g typescript
+```
+
+2. Переименовываем файл
+
+  > index.js -> index.ts
+
+3. Наблюдаем результат
+
+![screenshot](../assets/01.png)

01_simple/index.ts

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+const square = { width: 10, height: 10 };
+
+const check = () => console.log(square.width * square.heigth);

02_basic_config/src/index.ts

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+import { add } from './utils';
+
+const a = 1;
+const b = 22;
+
+console.info(add(a, b));

02_basic_config/src/utils.ts

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+export const add = (a: number, b: number) => a + b;

02_basic_config/tsconfig.json

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+{
+  "compilerOptions": {
+        "target": "es6",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
+        "module": "UMD",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
+        "outDir": "dist"
+    },
+    "files": [
+        "src/index.ts"
+    ],
+    "exclude": [
+        "node_modules",
+        "**/*.ts"
+    ]
+}

03_more_options/dist/index.d.ts

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+export {};

03_more_options/dist/index.js

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+import { add } from './utils';
+const a = 1;
+const b = 2;
+const c = 3;
+console.info(add(a, b));
+//# sourceMappingURL=index.js.map

03_more_options/dist/index.js.map

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+{"version":3,"file":"index.js","sourceRoot":"","sources":["../src/index.ts"],"names":[],"mappings":"AAAA,OAAO,EAAE,GAAG,EAAE,MAAM,SAAS,CAAC;AAE9B,MAAM,CAAC,GAAW,CAAC,CAAC;AACpB,MAAM,CAAC,GAAW,CAAC,CAAC;AACpB,MAAM,CAAC,GAAG,CAAC,CAAC;AAEZ,OAAO,CAAC,IAAI,CAAC,GAAG,CAAC,CAAC,EAAE,CAAC,CAAC,CAAC,CAAA"}

03_more_options/dist/utils.d.ts

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+export declare const add: (a: number, b: number) => string | number;
+interface Cat {
+    name?: {
+        fistName: string;
+        lastName: string;
+        age: number;
+    };
+}
+/**
+ * getCatName в консоль.
+ *
+ * @param {Cat} cat Сообщение.
+ * @param {number} notCat Тип сообщения.
+ */
+export declare const getCatName: (cat: Cat, notCat: number) => string | undefined;
+export {};

03_more_options/dist/utils.js

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+export const add = (a, b) => {
+    if (a > 0) {
+        return a + b;
+    }
+    return '' + a + b;
+};
+/**
+ * getCatName в консоль.
+ *
+ * @param {Cat} cat Сообщение.
+ * @param {number} notCat Тип сообщения.
+ */
+export const getCatName = (cat, notCat) => {
+    return cat.name && cat.name.fistName;
+};
+//# sourceMappingURL=utils.js.map

03_more_options/dist/utils.js.map

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+{"version":3,"file":"utils.js","sourceRoot":"","sources":["../src/utils.ts"],"names":[],"mappings":"AAAA,MAAM,CAAC,MAAM,GAAG,GAAG,CAAC,CAAS,EAAE,CAAS,EAAE,EAAE;IACxC,IAAI,CAAC,GAAG,CAAC,EAAE,CAAC;QACR,OAAO,CAAC,GAAG,CAAC,CAAA;IAChB,CAAC;IAED,OAAO,EAAE,GAAG,CAAC,GAAG,CAAC,CAAA;AACrB,CAAC,CAAA;AAUD;;;;;GAKG;AACH,MAAM,CAAC,MAAM,UAAU,GAAG,CAAC,GAAQ,EAAE,MAAc,EAAE,EAAE;IACnD,OAAO,GAAG,CAAC,IAAI,IAAI,GAAG,CAAC,IAAI,CAAC,QAAQ,CAAA;AACxC,CAAC,CAAA"}

03_more_options/src/index.ts

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+import { add } from './utils';
+
+const a: number = 1;
+const b: number = 2;
+const c = 3;
+
+console.info(add(a, b))

03_more_options/src/utils.ts

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+export const add = (a: number, b: number) => {
+    if (a > 0) {
+        return a + b
+    }
+
+    return '' + a + b
+}
+
+interface Cat {
+    name?: {
+        fistName: string;
+        lastName: string;
+        age: number;
+    }
+}
+
+/**
+ * getCatName в консоль.
+ *
+ * @param {Cat} cat Сообщение.
+ * @param {number} notCat Тип сообщения. 
+ */
+export const getCatName = (cat: Cat, notCat: number) => {
+    return cat.name && cat.name.fistName
+}

03_more_options/test.js

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+// @ts-check
+import { add } from './dist/utils'
+
+add(1, '2')

03_more_options/tsconfig.json

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+{
+  "compilerOptions": {
+    /* Basic Options */
+    "target": "ESNext",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017', 'ES2018', 'ES2019' or 'ESNEXT'. */
+    "module": "ESNext",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
+    "declaration": true,                   /* Generates corresponding '.d.ts' file. */
+    "sourceMap": true,                     /* Generates corresponding '.map' file. */
+    "outDir": "dist",                       /* Redirect output structure to the directory. */
+
+    // "noEmit": true,                        /* Do not emit outputs. */
+
+    /* Strict Type-Checking Options */
+    "strict": false,                           /* Enable all strict type-checking options. */
+    "noImplicitAny": true,                 /* Raise error on expressions and declarations with an implied 'any' type. */
+    "strictNullChecks": true,              /* Enable strict null checks. */
+
+    /* Additional Checks */
+    "noUnusedLocals": false,                /* Report errors on unused locals. */
+    "noUnusedParameters": false,            /* Report errors on unused parameters. */
+    "noImplicitReturns": false,             /* Report error when not all code paths in function return a value. */
+
+    /* Source Map Options */
+    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
+    },
+    "files": [
+        "src/index.ts"
+    ],
+    "exclude": [
+        "node_modules",
+        "**/*.ts"
+    ]
+}

04_lint/eslint.config.mjs

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+import globals from 'globals';
+import pluginJs from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+
+export default [
+  {files: ['**/*.{js,mjs,cjs,ts}']},
+  {languageOptions: { globals: globals.browser }},
+  pluginJs.configs.recommended,
+  ...tseslint.configs.recommended,
+  {
+    rules: {
+      quotes: ['error', 'single'],
+    }
+  }
+];

04_lint/example.ts

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+const boys = 32;
+const girls = 25;
+
+const summ = (a, b) => {
+    return a + b;
+}
+
+const boysAndGirls = summ(boys, girls);

04_lint/package.json

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+{
+  "name": "04_lint",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "license": "ISC",
+  "description": "",
+  "devDependencies": {
+    "@eslint/js": "^9.12.0",
+    "eslint": "^9.12.0",
+    "globals": "^15.10.0",
+    "typescript-eslint": "^8.8.1"
+  }
+}

04_lint/src/index.ts

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+import { logger } from './utils';
+import { MESSAGE_TYPE } from "./model";
+
+logger('good');
+logger("something is wrong", MESSAGE_TYPE.WARNING)
+logger('something is very wrong', MESSAGE_TYPE.ERROR);

04_lint/src/model/enums.ts

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+/**
+ * Тип сообщения.
+ *
+ * WARNING - Предупреждение.
+ * ERROR - Ошибка.
+ * SUCCESS - Успешно.
+ */
+export enum MESSAGE_TYPE {
+    WARNING = '#EA9325',
+    ERROR = '#FF3532',
+    SUCCESS = '#449D2C'
+}

04_lint/src/model/index.ts

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+export { MESSAGE_TYPE } from './enums';
+export { TMessage } from './types';

04_lint/src/model/types.ts

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+/**
+ * Сообщение.
+ */
+export type TMessage = string | number;

04_lint/src/utils/index.ts

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+export { logger } from './logUtils';

04_lint/src/utils/logUtils.ts

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+import { TMessage, MESSAGE_TYPE } from '../model';
+
+/**
+ * Логирует цветное сообщение в консоль.
+ *
+ * @param {TMessage} message Сообщение.
+ * @param {MESSAGE_TYPE} type Тип сообщения. 
+ */
+export const logger = (message: TMessage, type: MESSAGE_TYPE = MESSAGE_TYPE.SUCCESS): void => {
+    console.info(`%c ${message}`, `
+        color: ${type};
+        font-size: 25px;
+    `);
+};

05_error/animals.js

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+var __extends = (this && this.__extends) || (function () {
+    var extendStatics = function (d, b) {
+        extendStatics = Object.setPrototypeOf ||
+            ({ __proto__: [] } instanceof Array && function (d, b) { d.__proto__ = b; }) ||
+            function (d, b) { for (var p in b) if (Object.prototype.hasOwnProperty.call(b, p)) d[p] = b[p]; };
+        return extendStatics(d, b);
+    };
+    return function (d, b) {
+        if (typeof b !== "function" && b !== null)
+            throw new TypeError("Class extends value " + String(b) + " is not a constructor or null");
+        extendStatics(d, b);
+        function __() { this.constructor = d; }
+        d.prototype = b === null ? Object.create(b) : (__.prototype = b.prototype, new __());
+    };
+})();
+var Animal = /** @class */ (function () {
+    function Animal() {
+    }
+    return Animal;
+}());
+var Dog = /** @class */ (function (_super) {
+    __extends(Dog, _super);
+    function Dog() {
+        return _super !== null && _super.apply(this, arguments) || this;
+    }
+    Dog.prototype.bark = function () { };
+    return Dog;
+}(Animal));
+var Cat = /** @class */ (function (_super) {
+    __extends(Cat, _super);
+    function Cat() {
+        return _super !== null && _super.apply(this, arguments) || this;
+    }
+    Cat.prototype.meow = function () { };
+    return Cat;
+}(Animal));
+var cage1 = [new Dog(), new Dog()];
+var cage2 = cage1; // ok
+cage2.push(new Cat()); // ok
+cage1.forEach(function (dog) { return dog.bark(); }); // ok

05_error/animals.ts

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+class Animal {}
+class Dog extends Animal { bark() {} }
+class Cat extends Animal { meow() {} }
+
+const cage1 = [new Dog(), new Dog()];
+
+const cage2: Animal[] = cage1; // ok
+
+cage2.push(new Cat()); // ok
+
+cage1.forEach(dog => dog.bark()) // ok

05_error/links.md

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+# Links
+
+ - [Javascript Abstract Syntax Tree](https://www.jointjs.com/demos/abstract-syntax-tree)
+ - [ast explorer](https://astexplorer.net/)
+ - [ts ast viewer](https://ts-ast-viewer.com/#)

05_error/tsconfig.json

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+{
+  "compilerOptions": {
+    /* Visit https://aka.ms/tsconfig to read more about this file */
+
+    /* Projects */
+    // "incremental": true,                              /* Save .tsbuildinfo files to allow for incremental compilation of projects. */
+    // "composite": true,                                /* Enable constraints that allow a TypeScript project to be used with project references. */
+    // "tsBuildInfoFile": "./.tsbuildinfo",              /* Specify the path to .tsbuildinfo incremental compilation file. */
+    // "disableSourceOfProjectReferenceRedirect": true,  /* Disable preferring source files instead of declaration files when referencing composite projects. */
+    // "disableSolutionSearching": true,                 /* Opt a project out of multi-project reference checking when editing. */
+    // "disableReferencedProjectLoad": true,             /* Reduce the number of projects loaded automatically by TypeScript. */
+
+    /* Language and Environment */
+    "target": "es2016",                                  /* Set the JavaScript language version for emitted JavaScript and include compatible library declarations. */
+    // "lib": [],                                        /* Specify a set of bundled library declaration files that describe the target runtime environment. */
+    // "jsx": "preserve",                                /* Specify what JSX code is generated. */
+    // "experimentalDecorators": true,                   /* Enable experimental support for legacy experimental decorators. */
+    // "emitDecoratorMetadata": true,                    /* Emit design-type metadata for decorated declarations in source files. */
+    // "jsxFactory": "",                                 /* Specify the JSX factory function used when targeting React JSX emit, e.g. 'React.createElement' or 'h'. */
+    // "jsxFragmentFactory": "",                         /* Specify the JSX Fragment reference used for fragments when targeting React JSX emit e.g. 'React.Fragment' or 'Fragment'. */
+    // "jsxImportSource": "",                            /* Specify module specifier used to import the JSX factory functions when using 'jsx: react-jsx*'. */
+    // "reactNamespace": "",                             /* Specify the object invoked for 'createElement'. This only applies when targeting 'react' JSX emit. */
+    // "noLib": true,                                    /* Disable including any library files, including the default lib.d.ts. */
+    // "useDefineForClassFields": true,                  /* Emit ECMAScript-standard-compliant class fields. */
+    // "moduleDetection": "auto",                        /* Control what method is used to detect module-format JS files. */
+
+    /* Modules */
+    "module": "commonjs",                                /* Specify what module code is generated. */
+    // "rootDir": "./",                                  /* Specify the root folder within your source files. */
+    // "moduleResolution": "node10",                     /* Specify how TypeScript looks up a file from a given module specifier. */
+    // "baseUrl": "./",                                  /* Specify the base directory to resolve non-relative module names. */
+    // "paths": {},                                      /* Specify a set of entries that re-map imports to additional lookup locations. */
+    // "rootDirs": [],                                   /* Allow multiple folders to be treated as one when resolving modules. */
+    // "typeRoots": [],                                  /* Specify multiple folders that act like './node_modules/@types'. */
+    // "types": [],                                      /* Specify type package names to be included without being referenced in a source file. */
+    // "allowUmdGlobalAccess": true,                     /* Allow accessing UMD globals from modules. */
+    // "moduleSuffixes": [],                             /* List of file name suffixes to search when resolving a module. */
+    // "allowImportingTsExtensions": true,               /* Allow imports to include TypeScript file extensions. Requires '--moduleResolution bundler' and either '--noEmit' or '--emitDeclarationOnly' to be set. */
+    // "resolvePackageJsonExports": true,                /* Use the package.json 'exports' field when resolving package imports. */
+    // "resolvePackageJsonImports": true,                /* Use the package.json 'imports' field when resolving imports. */
+    // "customConditions": [],                           /* Conditions to set in addition to the resolver-specific defaults when resolving imports. */
+    // "noUncheckedSideEffectImports": true,             /* Check side effect imports. */
+    // "resolveJsonModule": true,                        /* Enable importing .json files. */
+    // "allowArbitraryExtensions": true,                 /* Enable importing files with any extension, provided a declaration file is present. */
+    // "noResolve": true,                                /* Disallow 'import's, 'require's or '<reference>'s from expanding the number of files TypeScript should add to a project. */
+
+    /* JavaScript Support */
+    // "allowJs": true,                                  /* Allow JavaScript files to be a part of your program. Use the 'checkJS' option to get errors from these files. */
+    // "checkJs": true,                                  /* Enable error reporting in type-checked JavaScript files. */
+    // "maxNodeModuleJsDepth": 1,                        /* Specify the maximum folder depth used for checking JavaScript files from 'node_modules'. Only applicable with 'allowJs'. */
+
+    /* Emit */
+    // "declaration": true,                              /* Generate .d.ts files from TypeScript and JavaScript files in your project. */
+    // "declarationMap": true,                           /* Create sourcemaps for d.ts files. */
+    // "emitDeclarationOnly": true,                      /* Only output d.ts files and not JavaScript files. */
+    // "sourceMap": true,                                /* Create source map files for emitted JavaScript files. */
+    // "inlineSourceMap": true,                          /* Include sourcemap files inside the emitted JavaScript. */
+    // "noEmit": true,                                   /* Disable emitting files from a compilation. */
+    // "outFile": "./",                                  /* Specify a file that bundles all outputs into one JavaScript file. If 'declaration' is true, also designates a file that bundles all .d.ts output. */
+    // "outDir": "./",                                   /* Specify an output folder for all emitted files. */
+    // "removeComments": true,                           /* Disable emitting comments. */
+    // "importHelpers": true,                            /* Allow importing helper functions from tslib once per project, instead of including them per-file. */
+    // "downlevelIteration": true,                       /* Emit more compliant, but verbose and less performant JavaScript for iteration. */
+    // "sourceRoot": "",                                 /* Specify the root path for debuggers to find the reference source code. */
+    // "mapRoot": "",                                    /* Specify the location where debugger should locate map files instead of generated locations. */
+    // "inlineSources": true,                            /* Include source code in the sourcemaps inside the emitted JavaScript. */
+    // "emitBOM": true,                                  /* Emit a UTF-8 Byte Order Mark (BOM) in the beginning of output files. */
+    // "newLine": "crlf",                                /* Set the newline character for emitting files. */
+    // "stripInternal": true,                            /* Disable emitting declarations that have '@internal' in their JSDoc comments. */
+    // "noEmitHelpers": true,                            /* Disable generating custom helper functions like '__extends' in compiled output. */
+    // "noEmitOnError": true,                            /* Disable emitting files if any type checking errors are reported. */
+    // "preserveConstEnums": true,                       /* Disable erasing 'const enum' declarations in generated code. */
+    // "declarationDir": "./",                           /* Specify the output directory for generated declaration files. */
+
+    /* Interop Constraints */
+    // "isolatedModules": true,                          /* Ensure that each file can be safely transpiled without relying on other imports. */
+    // "verbatimModuleSyntax": true,                     /* Do not transform or elide any imports or exports not marked as type-only, ensuring they are written in the output file's format based on the 'module' setting. */
+    // "isolatedDeclarations": true,                     /* Require sufficient annotation on exports so other tools can trivially generate declaration files. */
+    // "allowSyntheticDefaultImports": true,             /* Allow 'import x from y' when a module doesn't have a default export. */
+    "esModuleInterop": true,                             /* Emit additional JavaScript to ease support for importing CommonJS modules. This enables 'allowSyntheticDefaultImports' for type compatibility. */
+    // "preserveSymlinks": true,                         /* Disable resolving symlinks to their realpath. This correlates to the same flag in node. */
+    "forceConsistentCasingInFileNames": true,            /* Ensure that casing is correct in imports. */
+
+    /* Type Checking */
+    "strict": true,                                      /* Enable all strict type-checking options. */
+    // "noImplicitAny": true,                            /* Enable error reporting for expressions and declarations with an implied 'any' type. */
+    // "strictNullChecks": true,                         /* When type checking, take into account 'null' and 'undefined'. */
+    // "strictFunctionTypes": true,                      /* When assigning functions, check to ensure parameters and the return values are subtype-compatible. */
+    // "strictBindCallApply": true,                      /* Check that the arguments for 'bind', 'call', and 'apply' methods match the original function. */
+    // "strictPropertyInitialization": true,             /* Check for class properties that are declared but not set in the constructor. */
+    // "strictBuiltinIteratorReturn": true,              /* Built-in iterators are instantiated with a 'TReturn' type of 'undefined' instead of 'any'. */
+    // "noImplicitThis": true,                           /* Enable error reporting when 'this' is given the type 'any'. */
+    // "useUnknownInCatchVariables": true,               /* Default catch clause variables as 'unknown' instead of 'any'. */
+    // "alwaysStrict": true,                             /* Ensure 'use strict' is always emitted. */
+    // "noUnusedLocals": true,                           /* Enable error reporting when local variables aren't read. */
+    // "noUnusedParameters": true,                       /* Raise an error when a function parameter isn't read. */
+    // "exactOptionalPropertyTypes": true,               /* Interpret optional property types as written, rather than adding 'undefined'. */
+    // "noImplicitReturns": true,                        /* Enable error reporting for codepaths that do not explicitly return in a function. */
+    // "noFallthroughCasesInSwitch": true,               /* Enable error reporting for fallthrough cases in switch statements. */
+    // "noUncheckedIndexedAccess": true,                 /* Add 'undefined' to a type when accessed using an index. */
+    // "noImplicitOverride": true,                       /* Ensure overriding members in derived classes are marked with an override modifier. */
+    // "noPropertyAccessFromIndexSignature": true,       /* Enforces using indexed accessors for keys declared using an indexed type. */
+    // "allowUnusedLabels": true,                        /* Disable error reporting for unused labels. */
+    // "allowUnreachableCode": true,                     /* Disable error reporting for unreachable code. */
+
+    /* Completeness */
+    // "skipDefaultLibCheck": true,                      /* Skip type checking .d.ts files that are included with TypeScript. */
+    "skipLibCheck": true                                 /* Skip type checking all .d.ts files. */
+  }
+}

06_complex/infer.ts

@@ -0,0 +1,17 @@
+const arr = [1, 2, '3', 4, 5];
+// get type of array
+type GetArrItem<Arg> = Arg extends (infer Item)[] ? Item : never;
+
+type ArrItem = GetArrItem<typeof arr>
+
+const user = { name: 'John', age: 30 } as const;
+// get type of name property
+type GetObjectNameType<Name> = Name extends { name: infer T } ? T : never
+
+type UserName = GetObjectNameType<typeof user>
+
+const double = (x: number, s: 'foo') => x * 2;
+// get type of first argument of function
+type GetFirstFuncArg<Arg> = Arg extends (a, x: infer T) => any ? T : never;
+
+type DoubleArgType = GetFirstFuncArg<typeof double>