一句话

promise有点像OC的success的block和failure的block，resolve对应success，reject对应failure

下面，举个栗子：

static GET(url){
    return new Promise((resolve, reject)=>{
      fetch(url)
          .then(response=>response.json())
          .then(result=>{
            resolve(result);
          })
          .catch(error=>{
            reject(error);
          })
    })
  }

是不是很像oc的block，😀，比如用OC:

- (void)getUrl:(NSString *)url success:(void (^)(id))success failure:(void (^)(id))failure{
  //获取数据...
  
  if (success) {
    success(result);
  }
  
  if (failure) {
    failure(error);
  }
}

延伸下，fetch方法有点类似OC的Masonry，他们都属于链式语法

[view1 mas_makeConstraints:^(MASConstraintMaker *make) {
    make.left.equalTo(superview.mas_left).with.offset(padding.left);
}];