Question 286522 in Javascript Question posted in
A very good W3school tutorial can be found here.

Javascript – Is there a way to "remember" a past value of a variable?

Say I have a method that changes a value based on what the current value is. I will just make it very simple here:

  changeValue(){
    if(!this.value){
      this.value = 'value1'
    }
    else if(this.value === 'value1'){
      this.value = 'value2'
    }
    else if(this.value === 'value2'){
      this.value = 'value3'
    }
  },

And then I have another method that changes to a fourth value if the current value is either 2 or 3

  changeValues(){
    if(this.value === 'value2' || this.value === 'value3'){
      this.value = 'valueX'
    }
  },

Now I would like to add a click event that changes the value of valueX back to what it previously was, but I cannot specify it in the code, because the previous value could either be value2 or value3.

Is there a way to look at the variable "history", check what is previously was and then set it back to that?

  changeBack(){
    // if last value was value2 change back to value2
    // if last value was value3 then change back to value3
  }
Tags:

3

Answers


  1. 0 
    let valueHistory = [];
function changeValue(newValue) {
    valueHistory.push(this.value);
    this.value = newValue;
}
function changeBack() {
    if (valueHistory.length > 0) {
        this.value = valueHistory.pop();
    }
}
changeValue('hasanraza');
console.log(this.value);
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  2. 0

    Your question is tagged with vue.js, so my answer in vue

    You can use vue watchers and make a list and select them by their indexs or object with key: value pairs of all changes.

    data() {
  return {
    val: '',
    listOfValues: [],
  }
},
watch: {
  val(newVal, oldVal) {
    this.listOfValues.push(newVal)
    // or with if statement if you want to check
    if (...) {
    
    }
  }
},

    Vue Watchers

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  3. 0

    You can use an array to keep track of the history of values.

    Example:

    class YourClass {
  constructor() {
    this.value = null;
    this.valueHistory = [];
  }

  changeValue() {
    if (!this.value) {
      this.value = 'value1';
    } else if (this.value === 'value1') {
      this.value = 'value2';
    } else if (this.value === 'value2') {
      this.value = 'value3';
    }

    // Save the current value to history
    this.valueHistory.push(this.value);
  }

  changeValues() {
    if (this.value === 'value2' || this.value === 'value3') {
      this.value = 'valueX';
    }
  }

  changeBack() {
    // Pop the last value from history and set it as the current value
    if (this.valueHistory.length > 0) {
      this.value = this.valueHistory.pop();
    }
  }
}

    valueHistory is an array that keeps track of the history of values. The changeBack method pops the last value from the history array and sets it as the current value.

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