JavaScript strict mode

index.js

/**
 * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode#strict_mode_for_modules
 * @param a
 * @param b
 */
function esmIsStrictByDefault(a: number, b = 2) {
  return a + b;
}

/**
 * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode#strict_mode_for_functions
 * @param a
 */
function applyToBodyStrictParamsToBeSimple(a = 1) {
  'use strict';
  return a + 2;
}

/**
 * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Strict_mode#strict_mode_for_classes
 */
function classBodyIsInStrictMode() {
  class C1 {
    constructor() {
      delete Object.prototype;
    }
    test() {
      delete Object.prototype;
    }
  }

  const C2 = class {
    test() {
      // delete Object.prototype;
    }
  }
}
function assigningTOUndeclaredVariables() {
  // let mistypeVariable = 1;
  mistypeVariable = 12;
}

function failingToAssignToObjectProperties() {
  // NaN is non-writable global variable. In sloppy-mode, it does nothing,
  // in strict-mode, it throws an error.
  NaN = 1;
}

function failingToDeleteObjectProperties() {
  delete Object.prototype;
  delete [].length;

  var x;
  // Delete on a variable name
  delete x;
}

function duplicatePropertyNames() {
  const o = { p: 1, p: 2};
}

function removalOfTheWithStatement() {
  const x = 12;
  const obj = {};

  with(obj) {
    x = 23;
  }
}

function nonLeakingEval() {
  var x = 12;
  var evalX = eval("'use strict'; var x = 43; x");

  console.log(x);
  console.log(evalX);
}

function blockScopedFunction() {
  {
    function inner() {
      console.log('local function')
    }
  }

  inner();
}

function noThisSubstitution() {
  function returnThis() {
    return this;
  }

  console.assert(returnThis() === undefined);
  console.assert(returnThis.apply(null) === null);
  console.assert(returnThis.call(undefined) === undefined);
  console.assert(returnThis.bind(true)());
}

function removalOfStackWalkingProperties() {
  removalOfStackWalkingProperties.caller;
  removalOfStackWalkingProperties.arguments;
}