Map in JavaScript, ForEach

. Map (FN) method

1 var a=[2, 4, 6];2 a.map (function (d, I, arr) {3 return {x:i, y:d*i, z:arr};4});

Output Result:

1 [{x:0, y:0, Z:[2, 4, 6]}, 2 {x:1, Y:4, Z:[2, 4, 6]}, 3 {x:2, Y:12, Z:[2, 4, 6]}

The d in the callback function is the value of the traversal array, and I is the index of the array, and the entire array is passed in the third parameter.

Map casts the original array into a new array of the same length, and the value of each corresponding member in the new array is the value returned by the callback function.

The. ForEach (FN) method

1 var arr=[1, 3, 5];2 Arr.foreach (function (d, I, arr) {3 Console.log ([I, D, arr]); 4});

The results are as follows:

[0, 1, [1, 3, 5]] [0, 3, [1, 3, 5]] [0, 5, [1, 3, 5]]

Traverse arr, each pass in the values D and index I and the entire arr

Map in JavaScript, ForEach