A detailed introduction to using the bind() method in JavaScript to make the code cleaner

A few weeks ago, I wrote about how to turn off the effects of calling async functions in a loop and several ways to deal with this problem.

In my recent coding, I discovered an easier way. In the process, it eliminates anonymous functions and removes the linting error, "Don't write functions in loops".

You see, I've been experimenting with bind() in JavaScript. It turns out that we can use bind in multiple situations, including dealing with the closure problem I mentioned a few weeks ago.

What is bind()?

The bind function was only recently added to the JavaScript specification, so it only works on the latest browsers. You can check the compatibility matrix to see which browsers implement bind() and other JavaScript features. I looked at the list carefully, and none of the browsers I care about do not support bind(). Of course your situation may be different.

What bind does is automatically encapsulate the function in the function's own closure, so that we can bind the context (this keyword) and a series of parameters to the original function.

What you end up with is another function pointer.

function add(a,b){
    return a + b;
}
var newFoo = add.bind(this,3,4);

Please note that not only are we bundling this to the foo() function, but we are also bundling two parameters. So, when we call newFoo(), the return value will be 7.

But what happens if we change the parameters before calling newFoo?

Change the bind parameter

If we use a variable to bind the parameter to foo(), and then change the variable before calling newFoo(), you What do you think the value will be?

function add(a,b){
    return a + b;
}
var a = 3;
var b = 4;
var newFoo = add.bind(this,a, b);
a = 6;
b = 7;
console.log(newFoo());

The return value is still 7, because bind() binds the value of the parameter, not the value of the actual variable.

This is good news, like I said, we can take advantage of this huge advantage in our code. However, where it's most useful for me is in callbacks.

bind and callbacks

Remember from that article that one of our solutions for handling callbacks in a loop was to create anonymous functions around the function we wanted to call.

for(var i = 0;i < 10;i++){
    (function(ii){
        setTimeout(function(){
            console.log(ii);
        },1000);
    })(i);

But we can use bind to greatly simplify the code.

function consoleLog(i){
  console.log(i);
}
for(var i = 0;i < 10;i++){
    setTimeout(consoleLog.bind(this,i),1000);
}

This is because each time bind is called, a new function pointer is given and the original function remains unchanged.

At the same time, we also removed the linting error "Don't write functions in loops", because we did not create the function in the loop, we just pointed to the function we created outside the loop.

bind for event handlers

bind()Another place where you can make your code cleaner is in event handlers. Everyone knows, or should know, that when an event handler is called, it accesses the context in which the event was generated, not in the object in which the event handler was created. By using bind, you can be sure that the function will be accessed in the correct context.

function ClassName(){
   this.eventHandler = (function(){
   }).bind(this);
}

Not saying you should write code like that, it's just to illustrate the point.

Currying

What? !

OK. I'll be the first to admit that my knowledge of functional programming is limited. The best definition I can give of currying is that it allows you to pass parameters in multiple steps.

Using bind, we can write code like this to implement Currying:

function add(a,b,c) {
  return a+b+c;
}
var addAgain = add.bind(this, 1, 2);
var result = addAgain(3);

The above is a detailed introduction to using the bind() method in JavaScript to make the code cleaner. For more related information, please Follow the PHP Chinese website (www.php.cn)!