js bind implements

bind.js

let b = Function.prototype.bind
Function.prototype.bind = Function.prototype.bind || function bind(ctx) {
    let that = this
    let slice = Array.prototype.slice
    let bindArgs = slice.call(arguments,1)
    // bind可以传递参数，返回的被绑定的函数同样可以传参，所以这里先保存第一次bind的参数，忽略ctx，从 index 1 开始
    // 后面将调用时的参数传递进去，concat成一个array
    return function b(args) {
        // slice.call 将 arguments 转换为 Array
        that.apply(ctx,bindArgs.concat(slice.call(arguments)))
      // From https://stackoverflow.com/a/960870/7529562
      //NOTE: The slice function is intentionally generic; it does not require that its this value be an Array object. 
      //Therefore it can be transferred to other kinds of objects for use as a method.
      // Whether the slice function can be applied successfully to a host object is implementation-dependent.

      //Therefore, slice works on anything that has a length property, which arguments conveniently does.
    }
}

function test (a,b) {
    console.log(arguments)
}

let obj = {
    name: "wwc"
}

let newtest = test.bind(obj,'1','2')
newtest('3','4')