此值 = 未定義（打字稿）

Question

變量 this.engenes_comparte 出現在 subcribe 內為 undefined 但如果它有效，則出現在外面。

 baja(){    
  this._restService.getEngines(this._globalService.currentFisherMan.nid).subscribe((data : any[]) => {
    let state = 0;
        for (let index = 0; index <= data.length; index++) {
          for (let l = 0; l <= this.engines_compare.length; l++) {
            if(data[index].nid != this.engines_compare[l].nid){


            }
          }
        }
        console.log(this.engines_compare);
  });



  this.sube();
}

Answer 1

我無法理解你的程序的細節，但我想這是由於function(){ this }和() => {this}

this在允許功能有不同的含義this在function(){}風格的函數。

let A = {
   f() {
      return this.a // this is caller of f. This `this` is not always A. 
   }
   f2 = () => {
      return this.a // This `this` always equals A
   }
   a: 1
}
A.f() // => 1 because caller of f is A, so `this` is A.
A.f.call({}) // => undefined because caller of f is not A, but {}
A.f2() // => 2 
A.f2().call({}) // => 2 because this is always A