How to convert JavaScript function to work in typescript

Question

If I write it like this, I can't use this keyword

  LoadDrawing(drawing_name) {
    this.glg.LoadWidgetFromURL(drawing_name, null, this.LoadCB,drawing_name);
  }


  LoadCB(drawing, drawing_name) {
    if (drawing == null) {
     return;
    }   
    this.DrawingName = drawing_name;
    drawing.SetParentElement("glg_area");
  }

I dont know what to pass that drawing & drawing_name get same thing when pass using params

LoadDrawing(drawing_name) {
        this.glg.LoadWidgetFromURL(drawing_name, null, this.LoadCB(param1,param2),drawing_name);
      }

Well, not aware about glg but without demo I can't play the game of imagination! Good luck! — Prashant Pimpale
– Prashant Pimpale, Commented Dec 20, 2019 at 5:20

Will Taylor · Accepted Answer · 2019-12-20 07:20:08Z

2

You can preserve the this binding of LoadCB by defining it as an arrow function:

LoadDrawing(drawing_name) {
    this.glg.LoadWidgetFromURL(drawing_name, null, this.LoadCB,drawing_name);
}


LoadCB = (drawing, drawing_name) => {
    if (drawing == null) {
     return;
    }   
    this.DrawingName = drawing_name;
    drawing.SetParentElement("glg_area");
}

Note that this is nothing to do with TypeScript, but ES6 JavaScript classes.

ES6 class methods treat this bindings in the same way as a function defined using the function keyword does - in a way that is dependent on the call site rather than the lexical scope of the function. Arrow functions use lexical scope and so preserve the this binding in situations such as the above.

edited Dec 20, 2019 at 7:20

answered Dec 20, 2019 at 7:12

Will Taylor

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Mustafa Kunwa · Accepted Answer · 2019-12-20 07:02:48Z

0

Solved like this :

  LoadDrawing(drawing_name) {
        this.glg.LoadWidgetFromURL(drawing_name, null,(glg)=>this.LoadCB(glg,drawing_name),drawing_name);
      }    
      LoadCB(drawing, drawing_name) {
        if (drawing == null) {
         return;
        }   
        this.DrawingName = drawing_name;
        drawing.SetParentElement("glg_area");
      }

answered Dec 20, 2019 at 7:02

Mustafa Kunwa

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