js 手写call, apply, bind

  <script>
    Function.prototype.myCall = function () {
      var arg = Array.prototype.slice.call(arguments)
      var ctx = arg[0] || window
      var args = arg.slice(1)
      ctx._fn = this
      ctx._fn(...args)
      delete ctx._fn
    }
    Function.prototype.myApply = function () {
      var arg = Array.prototype.slice.call(arguments)
      var ctx = arg[0] || window
      var args = arg[1] || []
      ctx._fn = this
      ctx._fn(...args)
      delete ctx._fn
    }
    Function.prototype.myBind = function () {
      var arg = Array.prototype.slice.call(arguments)
      var ctx = arg[0] || window
      var args = arg.slice(1)
      ctx._fn = this
      return function () {
        args = args.concat(Array.prototype.slice.call(arguments))
        ctx._fn(...args)
        delete ctx._fn
      }
    }
    var b = 'c'
    var a = {
      b: 'b',
    }
    function m(k, j) {
      console.log(this.b);
      console.log(k);
      console.log(j);
    }
    // m('k', 'j') // c  k  j
    // m.myCall(a, 'k', 'j') // b  k  j
    // m.myApply(a, ['k', 'j']) // b  k  j
    // m.myBind(a, 'k')('j') // b  k  j
  </script>