How can I access data from a function that is executed within a method in Vue.js?

Question

How can I access data from a function that is executed within a method in Vue.js?

When working with vuejs and JS scopes, passing a value to a style property inside data can be tricky. The issue arises when trying to access this.data.property:

Vue.component ('loader-component', {
  template: '#loader-template',

  mounted: function() {
    this.animationTest();
  },

  data: function() {
    return {
      svg: true,
      timer: 0,
      // styles
      position: {
        marginLeft: '',
        marginTop: '',
        float: 'left'
      }
    };
  },

  methods: {
    animation: function() {
      let timer = 0,
          itemWidth = 60,
          domWidth = document.getElementById('awesome-body').clientWidth,
          domHeight = document.getElementById('awesome-body').clientHeight,
          marginL = -2 * itemWidth,
          marginT = Math.floor((Math.random() * domHeight) + 1);
          this.position.marginTop = marginT;
      setInterval(function() {
        marginL = marginL + timer * 5;
        timer++;
        // console.log(marginL);
        this.position.marginLeft = marginL;
      }, 1000); // time interval in milliseconds
    }
  } // methods finishes

});

This code snippet will result in the following error message:

Cannot set property 'marginLeft' of undefined.

Is there a specific syntax to directly access data.marginTop from the setInterval function?

Thank you!

javascript object this vue.js vuejs2

Answer 1

Answer №1

The this is actually pointing to the setInterval function, not the component itself. To fix this issue, try the following:

methods: {
    animateElements: function() {
        let element = this,
            count = 0,
            itemSize = 60,
            windowWidth = document.getElementById('amazing-layout').clientWidth,
            windowHeight = document.getElementById('amazing-layout').clientHeight,
            marginLeft = -2 * itemSize,
            marginTop = Math.floor((Math.random() * windowHeight) + 1);

        element.position.marginTop = marginTop;

        setInterval(function() {
            marginLeft = marginLeft + count * 5;
            count++;
            // console.log(marginLeft);
            element.position.marginLeft = marginLeft;
        }, 1000); // interval in milliseconds
    }
}

Answer 2

The this is actually pointing to the setInterval function, not the component itself. To fix this issue, try the following:

methods: {
    animateElements: function() {
        let element = this,
            count = 0,
            itemSize = 60,
            windowWidth = document.getElementById('amazing-layout').clientWidth,
            windowHeight = document.getElementById('amazing-layout').clientHeight,
            marginLeft = -2 * itemSize,
            marginTop = Math.floor((Math.random() * windowHeight) + 1);

        element.position.marginTop = marginTop;

        setInterval(function() {
            marginLeft = marginLeft + count * 5;
            count++;
            // console.log(marginLeft);
            element.position.marginLeft = marginLeft;
        }, 1000); // interval in milliseconds
    }
}

Answer 3

Answer №2

Perhaps considering a different approach would be beneficial in this situation. It appears that you are referencing an element that has not yet been rendered.

There are multiple methods available to achieve your desired outcome.

1/ Utilizing style binding

By using this method, you can bind data to the style of an element, which will automatically update your template when the data changes.

<template>
  <div :style="{ 'margin-left': whateverFunction() }">
  </div>
</template>

<script>
  ...
  methods: {
    whateverFunction () {
      return this.some_attribute + 'px'
    }
  }
  ...
</script>

Instead of a function, you can also use a computed property or an attribute for this purpose.

2/ Making use of the built-in transition system

If you wish to apply a transition to an element, the simplest way is to utilize the built-in transition system. Additionally, there are javascript hooks available for more control over the transition process.

3/ Using booleans and ref attributes creatively

If you need access to DOM elements within your code, consider utilizing booleans to ensure that your template is fully rendered before accessing them. You can also make use of the special ref attribute to easily retrieve the desired element.

If you require assistance with a specific part of your code, feel free to share a jsfiddle link for testing and debugging purposes.

Answer 4

Perhaps considering a different approach would be beneficial in this situation. It appears that you are referencing an element that has not yet been rendered.

There are multiple methods available to achieve your desired outcome.

1/ Utilizing style binding

By using this method, you can bind data to the style of an element, which will automatically update your template when the data changes.

<template>
  <div :style="{ 'margin-left': whateverFunction() }">
  </div>
</template>

<script>
  ...
  methods: {
    whateverFunction () {
      return this.some_attribute + 'px'
    }
  }
  ...
</script>

Instead of a function, you can also use a computed property or an attribute for this purpose.

2/ Making use of the built-in transition system

If you wish to apply a transition to an element, the simplest way is to utilize the built-in transition system. Additionally, there are javascript hooks available for more control over the transition process.

3/ Using booleans and ref attributes creatively

If you need access to DOM elements within your code, consider utilizing booleans to ensure that your template is fully rendered before accessing them. You can also make use of the special ref attribute to easily retrieve the desired element.

If you require assistance with a specific part of your code, feel free to share a jsfiddle link for testing and debugging purposes.

How can I access data from a function that is executed within a method in Vue.js?

Answer №1

Answer №2

1/ Utilizing style binding

2/ Making use of the built-in transition system

3/ Using booleans and ref attributes creatively

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