After triggering, VueJS will immediately run the watcher handler

Question

After triggering, VueJS will immediately run the watcher handler

Illustration:

export default {
    data() {
        return {
            value1: 1,
            value2: 2
        }
    },
    mounted() {
        this.value1 = 2
        console.log(this.value2)
    },
    watch: {
        value1: {
            handler(newValue1) {
                this.value2 = newValue1 * 3
            }
        }
    }
}

Anticipated outcome: the browser displays number 6 in the console

Current result: the browser displays number 2 in the console

In this scenario, I attempted to update the value of 'value2' after changing the value of 'value1', but it shows the original 'value2' instead of the modified one. Is there a method to immediately execute the watcher handler after triggering? I understand that for this example, computed properties can be utilized, however, I have specific data requirements in my project.

I made an effort to set the immediate property of the watcher to true, however, it did not work as expected.

javascript vue.js vue-component

Answer 1

Answer №1

To optimize your code, consider using a computed property for data2

export default {
            data() {
                return {
                    data1: 1
                }
            },
            mounted() {
                this.data1 = 2
                console.log(this.data2)
            },
            computed: {
              data2() {
                return this.data1 * 3 
              }
            }
         }

Answer 2

To optimize your code, consider using a computed property for data2

export default {
            data() {
                return {
                    data1: 1
                }
            },
            mounted() {
                this.data1 = 2
                console.log(this.data2)
            },
            computed: {
              data2() {
                return this.data1 * 3 
              }
            }
         }

Answer 3

Answer №2

The observer will not activate during the execution of your mounted() function; you must wait until the function has completed. This behavior is typical in JavaScript and is not specific to Vue.

Answer 4

The observer will not activate during the execution of your mounted() function; you must wait until the function has completed. This behavior is typical in JavaScript and is not specific to Vue.

Answer 5

Answer №3

When the browser runs, it outputs the number 2 to the console.

This occurs because Vue updates the DOM asynchronously during the first mount. When you make a change to data1 (and add console.log(this.data2) to the callback queue) at this point, this.data2 = 2 is set, resulting in the log of 2. It also triggers the watch on data1. If you log data2 here, you will see the value as 6.

To wait for Vue.js to finish updating the DOM after a data change, you can use Vue.nextTick(callback) right after changing the data.

mounted() {
  this.data1 = 2
  this.$nextTick(() => {
     console.log(this.data2); // 6
  })
}

Alternatively, you can use Vue.$watch to watch an expression or computed function on the Vue instance for changes:

data() {
  return {
    data1: 1,
    data2: 2
  }
},
watch: {
  data1: function(val) {
    this.data2 = val * 3
  }
},
mounted() {
  this.data1 = 2
  this.$watch('data2', (newVal) => {
    console.log(newVal) // 6
  })
}

Answer 6

When the browser runs, it outputs the number 2 to the console.

This occurs because Vue updates the DOM asynchronously during the first mount. When you make a change to data1 (and add console.log(this.data2) to the callback queue) at this point, this.data2 = 2 is set, resulting in the log of 2. It also triggers the watch on data1. If you log data2 here, you will see the value as 6.

To wait for Vue.js to finish updating the DOM after a data change, you can use Vue.nextTick(callback) right after changing the data.

mounted() {
  this.data1 = 2
  this.$nextTick(() => {
     console.log(this.data2); // 6
  })
}

Alternatively, you can use Vue.$watch to watch an expression or computed function on the Vue instance for changes:

data() {
  return {
    data1: 1,
    data2: 2
  }
},
watch: {
  data1: function(val) {
    this.data2 = val * 3
  }
},
mounted() {
  this.data1 = 2
  this.$watch('data2', (newVal) => {
    console.log(newVal) // 6
  })
}

Answer 7

Answer №4

Although I'm uncertain about the intention behind your code, the following modification should suffice:

  mounted() {
    this.value = 2
    this.$nextTick(() => {
      console.log(this.result)
    })
  },

Answer 8

Although I'm uncertain about the intention behind your code, the following modification should suffice:

  mounted() {
    this.value = 2
    this.$nextTick(() => {
      console.log(this.result)
    })
  },

Answer 9

Answer №5

In accordance with another solution, the default behavior is as expected and can usually be resolved by utilizing the nextTick method. However, in cases where a computed property is used instead, as proposed in yet another response, this may not always be necessary.

For Vue 3 users, there is an option to modify this behavior using the flush parameter:

mounted() {
    this.data1 = 2
    console.log(this.data2) // 6
},
watch: {
    data1: {
        handler(newData1) {
            this.data2 = newData1 * 3
        },
        flush: 'sync'
    }
}

Answer 10

In accordance with another solution, the default behavior is as expected and can usually be resolved by utilizing the nextTick method. However, in cases where a computed property is used instead, as proposed in yet another response, this may not always be necessary.

For Vue 3 users, there is an option to modify this behavior using the flush parameter:

mounted() {
    this.data1 = 2
    console.log(this.data2) // 6
},
watch: {
    data1: {
        handler(newData1) {
            this.data2 = newData1 * 3
        },
        flush: 'sync'
    }
}

After triggering, VueJS will immediately run the watcher handler

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Similar questions

Encountering the error message "Unable to locate module '.nextserverpages-manifest.json'" while attempting to include `babel.config.js` in a Next.js application

Silly problem arising from the animate feature in jQuery

What is the best way to locate a specific item within an array of objects, especially when each object has the potential to contain an array of objects of the

The dynamic duo of MongoDB and Prisma: forging a groundbreaking one-to-many relationship

Customizing Angular 2's Webpack environment setup dynamically

Introduce new router events, routeChangeStart and routeChangeComplete, within the client-side components of next js 14

Upon submission in Vue, the data variable becomes undefined

Clearing AsyncStorage in React Native

The component triggering the redirect prematurely, interrupting the completion of useEffect

Verification of email address is required, emails must be unique and not duplicated

What is the proper way to retrieve items from an Array that have an index that is evenly divisible by

Managing loading and changing events using Angular, jQuery, and Web API

The authentication middleware is being executed for all routes within my app.js file, despite my intention to only apply it to a single route

The Terser Plugin encounters compatibility issues when used with Vue CLI version 5 during the Vue build process

How to run a PHP script using JavaScript?

Convert JSON data into a compressed single row format

Utilizing the combineReducers() function yields disparate runtime outcomes compared to using a single reducer

Navigating through different components in React is made possible with React Router

Exporting modules from Node.js using Express framework is a common

Is there a way to reverse the JSON.stringify method?