Can you explain the significance of "..." in Angular2 and what purpose it serves?

Can you explain the use of "..." in Angular and what it is called? I am curious about why "...flash" is a parameter in the addFlash method within an array.push().

In the toggleFlash method, why is there "..." instead of using the this keyword?

flashs: IFlash[] = [];

flashs$ = new BehaviorSubject<IFlash[]>(this.flashs);

addFlash(flash: IFlash) {
    this.flashs.push({
        ...flash,
        show: false,
        id: getRandomNumber()
    });
}

toggleFlash(id: number) {
    const index = this.flashs.findIndex(flash => flash.id === id);
    this.flashs = [
        ...this.flashs.slice(0, index),
        {
            ...this.flashs[index],
            show: !this.flashs[index].show
        },
        ...this.flashs.slice(index + 1)
    ];
    this.flashs$.next(this.flashs);
}

Answer №1

... represents ES6 Spread Syntax in your code. When you use ...this.flashs, it will add all the items from this.flashs array to another array at the specified location. On the other hand, using {...this.flashs[index] will copy the properties of the object at the given index to another object where you are utilizing it. Refer to the comments within the code snippet below for a more detailed explanation.

 this.flashs = [
        ...this.flashs.slice(0, index), // Slicing flashs array and adding the resulting items here (e.g., obj1, obj2...)
        {
            ...this.flashs[index], // Obtain object at the specified index and incorporate its properties here (e.g., prop1: val, prop2: val,...)
            show: !this.flashs[index].show
        },
        ...this.flashs.slice(index + 1)
    ];

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