Differences between for in and for each in javascript: javascripteach

Differences between for in and for each in javascript: javascripteach

Difference 1:

For in is released in javascript 1.0.
For each in is released in javascript 1.6 as part of the E4X standard, and is not part of the ECMAScript standard.
This means there are compatibility issues with various browsers. For each in is not supported by many browsers. For example, Internet Explorer 6, Internet Explorer 7, and Internet Explorer 8 are not supported.

Difference 2:

For example, var rectangle = {Height: "15", width: "25 "};

For (var I in rectangle) {alert (I + "," + rectangle [I]);}

The results are as follows: height, 15; width, 25;

For each (var I in rectangle) {alert (I + "," + rectangle [I]);}

The results are as follows: 15, undefined; 25, undefined;

The values of variable I in the two traversal methods are different. for each in cannot obtain the attribute name of the object, and only the attribute value can be obtained.

Finally, we will summarize the usage suggestions:

(1) traverse common arrays. We recommend that you use the native Traversal method for. Do not greedy for the convenience of graphs, because for in and for each in both have browser compatibility problems, they cannot guarantee the traversal order of the array (if not required, you can use for in, but I do not recommend it, you can read the next article about defects of for in JavaScript.

(2) traverse objects. Because for cannot provide ideal traversal, you can only select other methods. We recommend that you use for in. From the difference described above, for in is more advantageous than for each. for in can obtain indexes and attribute values, while for each can only obtain attribute values, in addition, for each is not supported in many earlier browsers.

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