The Vue.JS countdown feature is malfunctioning

Question

The Vue.JS countdown feature is malfunctioning

My Vue application has a countdown feature that is not functioning correctly and I am not sure why.

When I view {{ $parent.timer }}, I can see the correct value.

Here is the data section of my Vue application:

data: function() {
      return {
         timer : 3,
...

Below is the countdown function I am using:

countdown : function(time,callback)
    {
         //time is equal 5
        this.timer = time;
        //this.timer is equal 5
        var timerInterval = undefined;

        timerInterval = setInterval(function() {
            if(this.timer == 1) {
                this.timer = 0;
                callback();
                return clearInterval(timerInterval);
            }
            // First time undefined, in 2nd is NaN
            this.timer -= 1;
            // NaN
        }, 1000);
    }

To call the function:

this.countdown(data.time,function(){ //smtng });

Can someone please help me figure out what I am doing wrong? This countdown function used to work in my previous Vue application.

Thank you in advance for any assistance!

javascript vue.js

Answer 1

Answer №1

One common issue is related to the scope of this, detailed as follows:

When using function() {...}, a new scope is created internally. Consequently, if this is used within this function, it does not refer to the outer scope. As a result, the this.timer of the Vue component may not be updated from inside the setInterval().

On the other hand, () => {...} behaves like a function without creating a new internal scope.

To resolve this issue, you can try the following code:

timerInterval = setInterval(() => {
    if(this.timer == 1) {
        this.timer = 0;  // `this` now points to the scope of the Vue component
        callback();
        // ...
    }
    // ...
}, 1000);

For more information on arrow functions, you can visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/Arrow_functions

Answer 2

One common issue is related to the scope of this, detailed as follows:

When using function() {...}, a new scope is created internally. Consequently, if this is used within this function, it does not refer to the outer scope. As a result, the this.timer of the Vue component may not be updated from inside the setInterval().

On the other hand, () => {...} behaves like a function without creating a new internal scope.

To resolve this issue, you can try the following code:

timerInterval = setInterval(() => {
    if(this.timer == 1) {
        this.timer = 0;  // `this` now points to the scope of the Vue component
        callback();
        // ...
    }
    // ...
}, 1000);

For more information on arrow functions, you can visit: https://developer.mozilla.org/en/docs/Web/JavaScript/Reference/Functions/Arrow_functions

The Vue.JS countdown feature is malfunctioning

Answer №1

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