How to call functions as parameters in javascript_javascript skills

The example in this article describes the method of calling functions as parameters in JavaScript. Share it with everyone for your reference. The specific analysis is as follows:

Let’s look at an example first:

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('01', 'abc');
m.put('02', 1024);
m.put('03', true);
m.put('04', 0);
m.put('05', false);

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

The order in which this code is executed is: interpreted and executed from top to bottom, which is a requirement of JS.
Here we mainly explain how the function in m.eachMap() is passed and executed as a parameter:

step1: When the m.eachMap method is executed, JS will find the corresponding this.eachMap method;
step2: Find the method this.eachMap and it will be executed according to the order of statements in the function body;
step3: When fn(attr, obj[attr]); is executed, it will return to the for statement execution; note that before returning to the for statement execution, attr has no value; after returning from the for statement, the value of attr is Yes, it is '01', and the value of obj[attr] is also there, it is 'abc';
step4: Then, fn(attr, obj[attr]); will return to the parameter function of the m.eachMap method, that is,

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

attr replaces key, obj[attr] replaces value, and executes the alert statement and outputs it.

Step5: Continue to execute the for loop, repeat step4, and output until the end.

I hope this article will be helpful to everyone’s JavaScript programming design.