A guide on iterating through an array in vue.js and appending a new attribute to each object

Question

A guide on iterating through an array in vue.js and appending a new attribute to each object

To incorporate a new property or array item into an existing virtual DOM element in Vue.js, the $set function must be utilized. Attempting to do so directly can cause issues:

For objects:
```
this.myObject.newProperty = "value";
```
For arrays: this.myArray[3] = object;

The correct way to accomplish this is as follows:

For objects:

this.$set(this.myObject, "newProperty", "value");

For arrays:
```
this.$set(this.myArray, 3, object);
```

An issue may arise when trying to set a property for all objects within an array using a loop:

for (var i = 0; i < this.myArray.length; i++) {
    this.myArray[i].newProperty = "value";
}

If you wish to utilize $set to modify properties of all objects within an array, what method should be employed?

javascript vue.js

Answer 1

Answer №1

Your code has been slightly adjusted and it now works as intended:

new Vue({
  el: "#app",
  data: {
    todos: [{
        text: "Learn JavaScript",
        done: false
      },
      {
        text: "Learn Vue",
        done: false
      },
      {
        text: "Play around in JSFiddle",
        done: true
      },
      {
        text: "Build something awesome",
        done: true
      }
    ]
  },
  methods: {
    toggle: function(todo) {
      todo.done = !todo.done
    },
    changeProperty1() {
      const val = 'A'
      // This part of the code has been optimized for efficiency
      for (var i = 0, length = this.todos.length; i < length; i++) {
        this.$set(this.todos[i], 'property1', val);
      }
    },
    changeProperty1Again() {
      for (todo of this.todos) {
        if (todo.property1) {
          todo.property1 = 'B'
        }
      }
    }
  },
  created() {

  }
})

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

del {
  color: rgba(0, 0, 0, 0.3);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <h2>Todos:</h2>
  <ol>
    <li v-for="todo in todos">
      <label>
        <input type="checkbox"
          v-on:change="toggle(todo)"
          v-bind:checked="todo.done">

        <del v-if="todo.done">
          {{ todo.text }}
        </del>
        <span v-else>
          {{ todo.text }}
        </span>
        <span>
          {{ todo.property1 }}
        </span>
      </label>
    </li>
  </ol>
  <button @click="changeProperty1">Click this first</button>
  <button @click="changeProperty1Again">Click this second</button>
</div>

I apologize for the long snippet, I just copied it over from JSFiddle :)

Answer 2

Your code has been slightly adjusted and it now works as intended:

new Vue({
  el: "#app",
  data: {
    todos: [{
        text: "Learn JavaScript",
        done: false
      },
      {
        text: "Learn Vue",
        done: false
      },
      {
        text: "Play around in JSFiddle",
        done: true
      },
      {
        text: "Build something awesome",
        done: true
      }
    ]
  },
  methods: {
    toggle: function(todo) {
      todo.done = !todo.done
    },
    changeProperty1() {
      const val = 'A'
      // This part of the code has been optimized for efficiency
      for (var i = 0, length = this.todos.length; i < length; i++) {
        this.$set(this.todos[i], 'property1', val);
      }
    },
    changeProperty1Again() {
      for (todo of this.todos) {
        if (todo.property1) {
          todo.property1 = 'B'
        }
      }
    }
  },
  created() {

  }
})

body {
  background: #20262E;
  padding: 20px;
  font-family: Helvetica;
}

#app {
  background: #fff;
  border-radius: 4px;
  padding: 20px;
  transition: all 0.2s;
}

li {
  margin: 8px 0;
}

h2 {
  font-weight: bold;
  margin-bottom: 15px;
}

del {
  color: rgba(0, 0, 0, 0.3);
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>

<div id="app">
  <h2>Todos:</h2>
  <ol>
    <li v-for="todo in todos">
      <label>
        <input type="checkbox"
          v-on:change="toggle(todo)"
          v-bind:checked="todo.done">

        <del v-if="todo.done">
          {{ todo.text }}
        </del>
        <span v-else>
          {{ todo.text }}
        </span>
        <span>
          {{ todo.property1 }}
        </span>
      </label>
    </li>
  </ol>
  <button @click="changeProperty1">Click this first</button>
  <button @click="changeProperty1Again">Click this second</button>
</div>

I apologize for the long snippet, I just copied it over from JSFiddle :)

Answer 3

Answer №2

When you find yourself repeatedly using

this.$set(this.myArray, 3, object);

in a loop with an index, consider making modifications to your object like this:

var newObject = Object.assign({}, this.myArray[i], {newProperty: 'value'} ); // Create an immutable object
this.$set(this.myArray, i, newObject);

However, keep in mind that calling $set for each iteration can be inefficient. A more efficient approach would be to use the map function to create a new object within the array:

const newArray = myArray.map(object => {
   return Object.assign({}, object, {newProperty: 'value'} );
   //or by ES6 spread operator
   return {...object, newProperty: 'value'};
});

After updating the array, trigger Vuejs to re-render the changes.

This alternative method should provide a better solution, but remember to consider how your specific context may affect the implementation!

Answer 4

When you find yourself repeatedly using

this.$set(this.myArray, 3, object);

in a loop with an index, consider making modifications to your object like this:

var newObject = Object.assign({}, this.myArray[i], {newProperty: 'value'} ); // Create an immutable object
this.$set(this.myArray, i, newObject);

However, keep in mind that calling $set for each iteration can be inefficient. A more efficient approach would be to use the map function to create a new object within the array:

const newArray = myArray.map(object => {
   return Object.assign({}, object, {newProperty: 'value'} );
   //or by ES6 spread operator
   return {...object, newProperty: 'value'};
});

After updating the array, trigger Vuejs to re-render the changes.

This alternative method should provide a better solution, but remember to consider how your specific context may affect the implementation!

Answer 5

Answer №3

If you're looking to enhance objects within an array by adding new properties, rather than replacing values within the array based on their index, you can achieve this with the following technique:

new Vue({
    el: '#demo',
    data: {
        myArray: [
            {id: 1},
            {id: 2},
            {id: 3},
            {id: 4},
            {id: 5}
        ]
    },
    methods: {
        addProperties() {
            for (var i = 0; i < this.myArray.length; i++) {
                this.$set(this.myArray[i], 'newProperty', 5 - i)
            }
        }
    }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="demo">
    <div v-for="item in myArray" :key="item.id">
        <span>{{item.id}}: </span>
        <span v-if="item.newProperty">{{item.newProperty}}</span>
    </div>
    <button @click="addProperties">Add Properties</button>
</div>

Answer 6

If you're looking to enhance objects within an array by adding new properties, rather than replacing values within the array based on their index, you can achieve this with the following technique:

new Vue({
    el: '#demo',
    data: {
        myArray: [
            {id: 1},
            {id: 2},
            {id: 3},
            {id: 4},
            {id: 5}
        ]
    },
    methods: {
        addProperties() {
            for (var i = 0; i < this.myArray.length; i++) {
                this.$set(this.myArray[i], 'newProperty', 5 - i)
            }
        }
    }
});

<script src="https://cdnjs.cloudflare.com/ajax/libs/vue/2.5.17/vue.js"></script>
<div id="demo">
    <div v-for="item in myArray" :key="item.id">
        <span>{{item.id}}: </span>
        <span v-if="item.newProperty">{{item.newProperty}}</span>
    </div>
    <button @click="addProperties">Add Properties</button>
</div>

Answer 7

Answer №4

This technique doesn't directly involve Vue, but rather relies on vanilla JavaScript:

arr.map(item => { return {...item, additionalProperty: "similarValueToRest"}});

Answer 8

This technique doesn't directly involve Vue, but rather relies on vanilla JavaScript:

arr.map(item => { return {...item, additionalProperty: "similarValueToRest"}});

A guide on iterating through an array in vue.js and appending a new attribute to each object

Answer №1

Answer №2

Answer №3

Answer №4

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