This point inside the function / change this point inside the function

intra-function this Point to

these this The direction of , It's determined when we call the function . The different calling methods determine this The direction of is different

Generally point to our caller .

Change function interior this Point to

call Method

call() Method calls an object . Simply understood as the way to call a function , But it can change the function this Point to

Application scenarios : Often do inheritance .

var o = {
    
	name: 'andy'
}
 function fn(a, b) {
    
      console.log(this);
      console.log(a+b)
};
fn(1,2)//  At this time this Pointing to window  The running result is 3
fn.call(o,1,2)// At this time this Point to the object o, Parameters are separated by commas , The running result is 3

The result of the above code is :

bind Method

bind() Methods do not call functions , But it can change the inside of the function this Point to , Return is the original function change this And the new functions that come out of it

If you just want to change this Point to , And when you don't want to call this function , have access to bind

Application scenarios : Don't call functions , But also want to change this Point to

 var o = {
    
 name: 'andy'
 };

function fn(a, b) {
    
	console.log(this);
	console.log(a + b);
};
var f = fn.bind(o, 1, 2); // Here f yes bind New function returned 
f();// Call new function  this Point to the object o  Parameters are separated by commas 

call、apply、bind The similarities and differences of the three

• Common ground : Can change this Point to

• Difference :

  • call and apply Will call functions , And change the inside of the function this Point to .
  • call and apply The parameters passed are different ,call Pass parameters separated by commas ,apply Pass... Using an array
  • bind Does not call function , You can change the inside of the function this Point to .

• Application scenarios

  1. call Often do inheritance .
  2. apply It's often related to arrays . For example, with the help of mathematical objects to achieve the maximum and minimum value of the array
  3. bind Don't call functions , But also want to change this Point to . For example, change the internal timer this Point to .