Methods for calling functions as parameters in JavaScript _javascript tips

The examples in this article describe the methods that functions in JavaScript invoke as arguments. Share to everyone for your reference. The specific analysis is as follows:

First look at the example:

function Map () {
var obj = {};

This.put = function (key, value) {
Obj[key] = value;
}

This.eachmap = function (fn) {for
(var attr in obj) {
fn (attr, obj[attr]);
}} var m = new Map ();
M.put (' The ', ' abc ');
M.put (' A ', 1024);
M.put (', true ');
M.put (' 0 ');
M.put (' A ', false);

M.eachmap (function (key, value) {
alert (key + ":" + value);
});

The order in which this code is executed is: to interpret execution from the top down, which is the rule of JS.
Here is a description of how the function in M.eachmap () is passed and executed as a parameter:

Step1: The implementation to m.eachmap this method, JS will go to find the corresponding this.eachmap this method;
Step2: Find the This.eachmap method, which is executed according to the order of the function body;
Step3: When executed to FN (attr, obj[attr]), he will return to the For statement execution; Note that attr is not a value until the return for statement is executed; After returning from the for statement, the attr value is ' 01 ', and Obj[attr] The value also has, for ' ABC ';
Step4: Then FN (attr, obj[attr]) will return to the parameter function of M.eachmap this method, i.e.

function (key, value) {
alert (key + ":" + value);
}

Attr replaces key,obj[attr] to replace value and execute alert statement, output.

STEP5: Continue to execute the For loop, repeat the STEP4, and output until the end.

I hope this article will help you with your JavaScript programming.