slice.js

--- package/package.json (excerpt) ---
{
  "name": "slice.js",
  "version": "1.1.1",
  "description": "nano version for slice of string and array like Python.",
  "main": "lib/index.js",
  "scripts": {
    "test": "jest",
    "build": "babel src --out-dir lib && npm run test"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/hustcc/slice.js.git"
  },
  "keywords": [
    "slice.js",
    "slice"
  ],
  "author": "hustcc",
  "license": "MIT",
  "bugs": {
    "url": "https://github.com/hustcc/slice.js/issues"
  },
  "homepage": "https://github.com/hustcc/slice.js#readme",
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.0",
    "babel-jest": "^21.2.0",
    "babel-preset-env": "^1.6.1",
    "coveralls": "^3.0.0",
    "jest": "^21.2.1"
  },
  "jest": {
    "testRegex": "(/test)\\.(ts|tsx|js)$",
    "moduleFileExtensions": [
      "ts",
      "tsx",
      "js",
      "json"
    ],
    "collectCoverage": true,
    "collectCoverageFrom": [
      "src/**/*.{js}",
      "!**/node_modules/**",
      "!**/vendor/**"
    ],
    "moduleDirectories": [
      "node_modules"
    ],
    "transform": {
      "^.+\\.js?$": "babel-jest"
    }
  }
}


--- package.json (entry) ---
{
  "name": "slice.js",
  "version": "1.1.1",
  "description": "nano version for slice of string and array like Python.",
  "main": "lib/index.js",
  "scripts": {
    "test": "jest",
    "build": "babel src --out-dir lib && npm run test"
  },
  "repository": {
    "type": "git",
    "url": "git+https://github.com/hustcc/slice.js.git"
  },
  "keywords": [
    "slice.js",
    "slice"
  ],
  "author": "hustcc",
  "license": "MIT",
  "bugs": {
    "url": "https://github.com/hustcc/slice.js/issues"
  },
  "homepage": "https://github.com/hustcc/slice.js#readme",
  "devDependencies": {
    "babel-cli": "^6.26.0",
    "babel-core": "^6.26.0",
    "babel-jest": "^21.2.0",
    "babel-preset-env": "^1.6.1",
    "coveralls": "^3.0.0",
    "jest": "^21.2.1"
  },
  "jest": {
    "testRegex": "(/test)\\.(ts|tsx|js)$",
    "moduleFileExtensions": [
      "ts",
      "tsx",
      "js",
      "json"
    ],
    "collectCoverage": true,
    "collectCoverageFrom": [
      "src/**/*.{js}",
      "!**/node_modules/**",
      "!**/vendor/**"
    ],
    "moduleDirectories": [
      "node_modules"
    ],
    "transform": {
      "^.+\\.js?$": "babel-jest"
    }
  }
}


--- index.js (entry) ---
/**
 * 抛出一个异常
 * @param condition
 * @param s
 */
const invariant = (condition, s) => {
  if (!condition) throw new Error(s);
};

/**
 * 模仿 Python 的分片操作
 * @param v
 * @param start
 * @param end
 * @param step
 * @returns {Array}
 */
const slice = (v, start, end, step) => {
  const r = [];
  let i;
  if (step > 0) {
    for (i = start; i < end; i += step) {
      r.push(v[i]);
    }
  } else {
    for (i = start; i > end; i += step) {
      r.push(v[i]);
    }
  }
  return r;
};

/**
 * parse a string / number to number.
 *
 * parseInt('') === NaN
 * Number('') === 0
 * @param n
 */
const parseNumber = n => isNaN(parseInt(n)) ? NaN : Number(n);

/**
 * parse slice string
 * start:end:stepß
 * @param path
 * @param l
 * @returns {*[]}
 */
const parseSliceString = (path, l) => {
  let [start, end, step] = path.split(':').map(s => parseNumber(s));
  // 异常的时候默认值
  start = isNaN(start) ? 0 :
    start < 0 ? l + start : start;

  end = isNaN(end) ? l :
    end < 0 ? l + end : // 小于 0 转成正数
      end > l ? l : end; // 最大为长度

  step = isNaN(step) ? 1 : step;

  invariant(step !== 0, 'Step can not be zero!');

  return [
    start,
    end,
    step,
  ];
};

/**
 * slice entry 方法
 * @param