正确绑定到 Javascript 函数参数

Question

I got a method which receives 2 parameters:

function func(param1, param2){...

I got a React component which receives a function as a parameter and it has the information about the 2nd parameter, and I want to set the first parameter in this case as a constant.

What I'm doing is:

let myFuncToPass = func.bind("const value", null);
.
.
.
<ComponentName funcParam = { (res) => myFuncToPass(res) } 
.

I was expecting that when the callback is invoked, the parameter will be called with "const value" as the first parameter and the res as the 2nd. What happens is that the res is received as it should to the 2nd parameter, but the first one is null instead of "const value"

What did I do wrong here?

Answer 1

I think you want to do this:

let myFuncToPass = func.bind(this, "const value");

[edit] the first argument won't necessarily be this , it depends entirely on your usecase -- if func never uses this internally it probably doesn't matter at all, or you may prefer to pass null in -- you'll need to think about that question for yourself

the first argument binds what this means when the resulting function is called, and the second argument defines the first argument passed to the function

[edit]

Just do this as an experiment:

function x() {
  console.log(this);
  console.log(arguments);
}

x();

x.bind({a:2}, "first argument")("second argument");

Answer 2

Look to docs: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_objects/Function/bind

Bind function first parameter is this .

To use a partial application, you should use babel or a functional library like Ramdajs or write like this.

func.bind('irrelevant', 'const value')