function from(arrayLike
      /*, mapFn, thisArg */
      ) {
        // 1. Let C be the this value.
        var C = this; // 2. Let items be ToObject(arrayLike).

        var items = Object(arrayLike); // 3. ReturnIfAbrupt(items).

        if (arrayLike == null) {
          throw new TypeError('Array.from requires an array-like object - not null or undefined');
        } // 4. If mapfn is undefined, then let mapping be false.


        var mapFn = arguments.length > 1 ? arguments[1] : void undefined;
        var T;

        if (typeof mapFn !== 'undefined') {
          // 5. else
          // 5. a If IsCallable(mapfn) is false, throw a TypeError exception.
          if (!isCallable(mapFn)) {
            throw new TypeError('Array.from: when provided, the second argument must be a function');
          } // 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined.


          if (arguments.length > 2) {
            T = arguments[2];
          }
        } // 10. Let lenValue be Get(items, "length").
        // 11. Let len be ToLength(lenValue).


        var len = toLength(items.length); // 13. If IsConstructor(C) is true, then
        // 13. a. Let A be the result of calling the [[Construct]] internal method
        // of C with an argument list containing the single item len.
        // 14. a. Else, Let A be ArrayCreate(len).

        var A = isCallable(C) ? Object(new C(len)) : new Array(len); // 16. Let k be 0.

        var k = 0; // 17. Repeat, while k < len… (also steps a - h)

        var kValue;

        while (k < len) {
          kValue = items[k];

          if (mapFn) {
            A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
          } else {
            A[k] = kValue;
          }

          k += 1;
        } // 18. Let putStatus be Put(A, "length", len, true).


        A.length = len; // 20. Return A.

        return A;
      }
// The length property of the from method is 1.
The length property of the from method is 1.
The length property of the from method is 1 .
function from(arrayLike
      ) {
        var C = this; 
        var items = Object(arrayLike); 
        if (arrayLike == null) {
          throw new TypeError('Array.from requires an array-like object - not null or undefined');
        } 
        var mapFn = arguments.length > 1 ? arguments[1] : void undefined;
        var T;
        if (typeof mapFn !== 'undefined') {
          if (!isCallable(mapFn)) {
            throw new TypeError('Array.from: when provided, the second argument must be a function');
          } 
          if (arguments.length > 2) {
            T = arguments[2];
          }
        } 
        var len = toLength(items.length); 
        var A = isCallable(C) ? Object(new C(len)) : new Array(len); 
        var k = 0; 
        var kValue;
        while (k < len) {
          kValue = items[k];
          if (mapFn) {
            A[k] = typeof T === 'undefined' ? mapFn(kValue, k) : mapFn.call(T, kValue, k);
          } else {
            A[k] = kValue;
          }
          k += 1;
        } 
        A.length = len; 
        return A;
      }
function from ( arrayLike ) { var C = this ; var items = Object ( arrayLike ) ; if ( arrayLike == null ) { throw new TypeError ( 'Array.from requires an array-like object - not null or undefined' ) ; } var mapFn = arguments . length > 1 ? arguments [ 1 ] : void undefined ; var T ; if ( typeof mapFn !== 'undefined' ) { if ( ! isCallable ( mapFn ) ) { throw new TypeError ( 'Array.from: when provided, the second argument must be a function' ) ; } if ( arguments . length > 2 ) { T = arguments [ 2 ] ; } } var len = toLength ( items . length ) ; var A = isCallable ( C ) ? Object ( new C ( len ) ) : new Array ( len ) ; var k = 0 ; var kValue ; while ( k < len ) { kValue = items [ k ] ; if ( mapFn ) { A [ k ] = typeof T === 'undefined' ? mapFn ( kValue , k ) : mapFn . call ( T , kValue , k ) ; } else { A [ k ] = kValue ; } k += 1 ; } A . length = len ; return A ; }
The length property of the from method is 1.
The length property of the from method is 1 .
/*, mapFn, thisArg */ // 1. Let C be the this value. // 2. Let items be ToObject(arrayLike). // 3. ReturnIfAbrupt(items). // 4. If mapfn is undefined, then let mapping be false. // 5. else // 5. a If IsCallable(mapfn) is false, throw a TypeError exception. // 5. b. If thisArg was supplied, let T be thisArg; else let T be undefined. // 10. Let lenValue be Get(items, "length"). // 11. Let len be ToLength(lenValue). // 13. If IsConstructor(C) is true, then // 13. a. Let A be the result of calling the [[Construct]] internal method // of C with an argument list containing the single item len. // 14. a. Else, Let A be ArrayCreate(len). // 16. Let k be 0. // 17. Repeat, while k < len… (also steps a - h) // 18. Let putStatus be Put(A, "length", len, true). // 20. Return A.