call ,bind, promise 模仿实现原理_promise bind

call 的实现原理

Function.prototype.mycall = function (target){
      target=target || window;
      target.fun = this;
      const arg = [...arguments].slice(1);
      const rut = target.fun(arg);
      delete target.fun;
      retuan rut;
}
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bind 的实现原理

Function.prototype.mybind = function(content){
    if(typeof this !== "function"){
       return
    }
    content = content || window;
    let args = [...arguments].slice(1)||""
    content.fun = this;
    return (function(args){
       return function(...b){
            let a = [...args,...b]
            content.fun(...a)
       }
    })(args)
}
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Promise 简单实现原理

class MyPromise{
    constructor(arg){
        this.res;
        this.rej;
        this.callThis();
        this.value = null;
        agr(this.res,this.rej);
    }
    callThis(){
        this.res = this.resolve;
        this.rej = this.resject;
    }
    resolve(success){
       this.value = success;
    }
    resject(error){
        this.value = error;
    }
    then(fun){
       fun(this.value);
    }
}
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