Benchmark files for https://qiita.com/kyokoshimizu/items/40fa64f29efcbcddfc49

package.json

{
  "scripts": {
    "start": "tsc && node test.js"
  },
  "dependencies": {
    "@types/node": "^10.12.12",
    "lodash": "^4.17.11",
    "typescript": "^3.2.2"
  },
  "devDependencies": {
    "@types/lodash": "^4.14.118"
  }
}

test.ts

import * as _ from 'lodash'
import {performance} from 'perf_hooks'

let data1: { a: number, b: number[] }[] = [];
let data2: { a: number, b: number[] }[] = [];
let data3: { a: number, b: number[] }[] = [];

Array.from({ length: 10000 }, (_) => {
  const num = Math.random();
  data1.push({ a: num, b: [1,2,3] });
  data2.push({ a: num, b: [1,2,3] });
  data3.push({ a: num, b: [1,2,3] });
});

const pureJS = (data: { a: number, b: number[] }[]) => {
  const start_ms = performance.now();
  data.map((o) => { return o.b })
    .reduce((a, b) => a.concat(b), []);
  return performance.now() - start_ms;
}

const pureJS2 = (data: { a: number, b: number[] }[]) => {
  const start_ms = performance.now();
  ([] as number[]).concat(...data.map((o) => { return o.b }))
  return performance.now() - start_ms;
}

const lodash = (data: { a: number, b: number[] }[]) => {
  const start_ms = performance.now();
  _.chain(data).map('b')
    .flatten().value();
  return performance.now() - start_ms;
}

let result1: number[] = [];
let result2: number[] = [];
let result3: number[] = [];
Array.from({ length: 10 }, (_) => {
  result1.push(pureJS(data1));
  result2.push(lodash(data2));
  result3.push(pureJS2(data2));
});
console.log('PureJS(ms):  ' + _.sum(result1) / 10);
console.log('Lodash(ms):  ' + _.sum(result2) / 10);
console.log('PureJS2(ms): ' + _.sum(result3) / 10);

tsconfig.json

{
  "compilerOptions": {
    /* Basic Options */
    "target": "es2015",                          /* Specify ECMAScript target version: 'ES3' (default), 'ES5', 'ES2015', 'ES2016', 'ES2017','ES2018' or 'ESNEXT'. */
    "module": "commonjs",                     /* Specify module code generation: 'none', 'commonjs', 'amd', 'system', 'umd', 'es2015', or 'ESNext'. */
    // "lib": [],                             /* Specify library files to be included in the compilation. */
    // "allowJs": true,                       /* Allow javascript files to be compiled. */
    // "checkJs": true,                       /* Report errors in .js files. */
    // "jsx": "preserve",                     /* Specify JSX code generation: 'preserve', 'react-native', or 'react'. */
    // "declaration": true,                   /* Generates corresponding '.d.ts' file. */
    // "declarationMap": true,                /* Generates a sourcemap for each corresponding '.d.ts' file. */
    // "sourceMap": true,                     /* Generates corresponding '.map' file. */
    // "outFile": "./",                       /* Concatenate and emit output to single file. */
    // "outDir": "./",                        /* Redirect output structure to the directory. */
    // "rootDir": "./",                       /* Specify the root directory of input files. Use to control the output directory structure with --outDir. */
    // "composite": true,                     /* Enable project compilation */
    // "removeComments": true,                /* Do not emit comments to output. */
    // "noEmit": true,                        /* Do not emit outputs. */
    // "importHelpers": true,                 /* Import emit helpers from 'tslib'. */
    // "downlevelIteration": true,            /* Provide full support for iterables in 'for-of', spread, and destructuring when targeting 'ES5' or 'ES3'. */
    // "isolatedModules": true,               /* Transpile each file as a separate module (similar to 'ts.transpileModule'). */

    /* Strict Type-Checking Options */
    "strict": true,                           /* 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. */
    // "strictFunctionTypes": true,           /* Enable strict checking of function types. */
    // "strictBindCallApply": true,           /* Enable strict 'bind', 'call', and 'apply' methods on functions. */
    // "strictPropertyInitialization": true,  /* Enable strict checking of property initialization in classes. */
    // "noImplicitThis": true,                /* Raise error on 'this' expressions with an implied 'any' type. */
    // "alwaysStrict": true,                  /* Parse in strict mode and emit "use strict" for each source file. */

    /* Additional Checks */
    // "noUnusedLocals": true,                /* Report errors on unused locals. */
    // "noUnusedParameters": true,            /* Report errors on unused parameters. */
    // "noImplicitReturns": true,             /* Report error when not all code paths in function return a value. */
    // "noFallthroughCasesInSwitch": true,    /* Report errors for fallthrough cases in switch statement. */

    /* Module Resolution Options */
    // "moduleResolution": "node",            /* Specify module resolution strategy: 'node' (Node.js) or 'classic' (TypeScript pre-1.6). */
    // "baseUrl": "./",                       /* Base directory to resolve non-absolute module names. */
    // "paths": {},                           /* A series of entries which re-map imports to lookup locations relative to the 'baseUrl'. */
    // "rootDirs": [],                        /* List of root folders whose combined content represents the structure of the project at runtime. */
    // "typeRoots": [],                       /* List of folders to include type definitions from. */
    // "types": [],                           /* Type declaration files to be included in compilation. */
    // "allowSyntheticDefaultImports": true,  /* Allow default imports from modules with no default export. This does not affect code emit, just typechecking. */
    "esModuleInterop": true                   /* Enables emit interoperability between CommonJS and ES Modules via creation of namespace objects for all imports. Implies 'allowSyntheticDefaultImports'. */
    // "preserveSymlinks": true,              /* Do not resolve the real path of symlinks. */

    /* Source Map Options */
    // "sourceRoot": "",                      /* Specify the location where debugger should locate TypeScript files instead of source locations. */
    // "mapRoot": "",                         /* Specify the location where debugger should locate map files instead of generated locations. */
    // "inlineSourceMap": true,               /* Emit a single file with source maps instead of having a separate file. */
    // "inlineSources": true,                 /* Emit the source alongside the sourcemaps within a single file; requires '--inlineSourceMap' or '--sourceMap' to be set. */

    /* Experimental Options */
    // "experimentalDecorators": true,        /* Enables experimental support for ES7 decorators. */
    // "emitDecoratorMetadata": true,         /* Enables experimental support for emitting type metadata for decorators. */
  }
}

yarn.lock

# THIS IS AN AUTOGENERATED FILE. DO NOT EDIT THIS FILE DIRECTLY.
# yarn lockfile v1


"@types/lodash@^4.14.118":
  version "4.14.118"
  resolved "https://registry.yarnpkg.com/@types/lodash/-/lodash-4.14.118.tgz#247bab39bfcc6d910d4927c6e06cbc70ec376f27"
  integrity sha512-iiJbKLZbhSa6FYRip/9ZDX6HXhayXLDGY2Fqws9cOkEQ6XeKfaxB0sC541mowZJueYyMnVUmmG+al5/4fCDrgw==

"@types/node@^10.12.12":
  version "10.12.12"
  resolved "https://registry.yarnpkg.com/@types/node/-/node-10.12.12.tgz#e15a9d034d9210f00320ef718a50c4a799417c47"
  integrity sha512-Pr+6JRiKkfsFvmU/LK68oBRCQeEg36TyAbPhc2xpez24OOZZCuoIhWGTd39VZy6nGafSbxzGouFPTFD/rR1A0A==

lodash@^4.17.11:
  version "4.17.11"
  resolved "https://registry.yarnpkg.com/lodash/-/lodash-4.17.11.tgz#b39ea6229ef607ecd89e2c8df12536891cac9b8d"
  integrity sha512-cQKh8igo5QUhZ7lg38DYWAxMvjSAKG0A8wGSVimP07SIUEK2UO+arSRKbRZWtelMtN5V0Hkwh5ryOto/SshYIg==

typescript@^3.2.2:
  version "3.2.2"
  resolved "https://registry.yarnpkg.com/typescript/-/typescript-3.2.2.tgz#fe8101c46aa123f8353523ebdcf5730c2ae493e5"
  integrity sha512-VCj5UiSyHBjwfYacmDuc/NOk4QQixbE+Wn7MFJuS0nRuPQbof132Pw4u53dm264O8LPc2MVsc7RJNml5szurkg==

$ node -v
v11.1.0

$ yarn start
yarn run v1.12.1
$ tsc && node test.js
PureJS(ms):  199.43697868585588
Lodash(ms):  1.7742313146591187
PureJS2(ms): 0.40608648061752317
Done in 4.08s.