Issue with setTimeout() function not being triggered within a VueJS method

I am currently developing an application that allows a user to reset or shutdown a particular server. I am focused on creating the interface and ensuring that the user receives appropriate messages about the actions being taken. My approach involves displaying a predefined message from a data object to communicate the action being executed. I then utilize setTimeout to toggle between displaying a "resetting..." message and a "reset" message. Below is the method I am using:

    systemReset: function(){
            this.message = this.server + ': Resetting';
            setTimeout(function(){
                this.message = this.server + ': Reset';
            }, 2000);
            
    } 

When testing this in my browser, the initial "Resetting" message appears as expected, but the subsequent "Reset" message is not displayed. Are there any errors in my formatting that might be causing this issue?

For better understanding, here is the complete component code:

  <template>
    <div>
      <p>{{message}}</p>
      <button @click="systemReset">Reset Server</button>
      <button @click="systemPowerDown">Poweroff Server</button>
    </div>
  </template>

  <script type="text/javascript">
    export default{
      data: function(){
        return{
          message: ''
        }
      },
      methods: {
        systemPowerDown: function(){
            this.message = this.server + ': Server Down';
        },
        systemReset: function(){
            this.message = this.server + ': Resetting';
            setTimeout(function(){
                this.message = this.server + ': Reset';
            }, 2000);
         }
      },
      props: ['server']
    }
  </script>

Am I overlooking something obvious? Could there be a Vue limitation that I am not aware of?  

Answer №1

When it comes to the setTimeout function, the value of this behaves differently.

In ES6, you have the option to utilize an arrow function:

setTimeout(() => { this.message = this.server + ': Reset' }, 2000)

If you are not using ES6, you can still manage the value of this by binding it:

setTimeout(function () {
  this.message = this.server + ': Reset'
}.bind(this))

However, without prior experience with Vue, it remains unclear as to whether it will automatically re-render upon changes to this.message, or if adjustments need to be made to some component's state.

Answer №2

When you are working within a setTimeout function, the context of this does not refer to your Vue instance. To resolve this issue, you can assign self as shown below:

systemReset: function(){
    this.message = this.server + ': Resetting';
    var self = this;
    setTimeout(function(){
        self.message = self.server + ': Reset';
    }, 2000);
}

Answer №3

Is it possible to address the issue by storing the value of this in a variable outside of the timeout function?

For example:

 systemReset: function(){
            var $this = this;
            $this.message = this.server + ': Resetting';
            setTimeout(function(){
                $this.message = this.server + ': Reset';
            }, 2000);
         }

This approach ensures that the proper function systemReset is referenced.

Answer №4

Encountering a common issue, I decided to develop a new function within the 'methods' section to adjust the variable accordingly. By invoking this method in the 'setInterval', I was able to resolve the problem effectively.

Answer №5

If all else fails, try using $forceUpdate().

Even though passing this to setTimeout() works in JSFiddle https://jsfiddle.net/BeloglazovRL/owL94phz/ (Vue 2.6.14), it doesn't seem to work with my web application that uses Vue 2.6.13.

After trying various solutions like saving this to self, using arrow functions, and explicit bind, I found that only calling this.$forceUpdate(); within the periodic setTimeout() helped update the screen.

Although the debug output indicated changes in variables and correct usage of this with Vue internal components, the actual screen didn't update until after the timer elapsed. I even extended the timeout duration to 5 seconds instead of 1 second, but it made no difference. Finally, resorting to a force update was the key. Referencing helpful insights from resources like Can you force Vue.js to reload/re-render?.

Implementing the solution involved updating the code structure as follows:

myTimer() {

  ... //Alter text, adjust timer, etc. Check for any stop conditions.

  this.vueTextVar = newUpdatedValue;
  this.$forceUpdate();
  setTimeout(() => {
          this.myTimer();
        }, 1000);
}

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