The error message "reverseMessage is not a function" occurred in Vue.JS

Question

The error message "reverseMessage is not a function" occurred in Vue.JS

I am attempting to show a string in reverse order using Vue. My template code is as follows:

<div id="app">
  <reverse :msgreverse="message" :reverseMessage="reverseMessage()"></reverse>
</div>

Here is my script:

function reverseMessage(msg) {
  return msg.split('').reverse().join('')
}

Vue.component('reverse', {
  props:["msgreverse", "reverseMessage"],
  template: '<p v-html="reverseMessage(msgreverse)"></p>'
})

var app = new Vue({
  el: '#app',
  data: {
    message:'The message to reverse !',
  }
})

However, when running this code, I encounter the following errors in the console:

TypeError: reverseMessage is not a function. (In 'reverseMessage()', 'reverseMessage' is undefined)
Error in render: "TypeError: reverseMessage is not a function. (In 'reverseMessage()', 'reverseMessage' is undefined)"
Property or method "reverseMessage" is not defined on the instance but referenced during render. Make sure that this property is reactive, either in the data option, or for class-based components, by initializing the property

Can someone advise me on how to make the <reverse> component display a given string in reverse?

javascript vue.js vuejs2

Answer 1

Answer №1

The issue at hand is that Vue is not recognizing the global function you have created (i.e., reverseMessage()). Vue does not have visibility over global functions or variables during template rendering. Local functions, on the other hand, can be accessed within the component's methods property. In your scenario, it should be structured like this:

Vue.component('reverse', {
  // ...
  methods: {
    reverseMessage(msg) {
      return msg.split('').reverse().join('')
    }
  }
})

Given that the component is intended for string reversal, there is no necessity for a prop to be allocated for the reverseMessage function. Thus, you can eliminate it from props:

Vue.component('reverse', {
  // ...
  //props:["msgreverse", "reverseMessage"],  // AVOID THIS
  props:["msgreverse"],
})

Your template is employing the v-html directive to display the reversed message, but this is unnecessary because (1) the message itself is not in HTML format, and (2) Vue discourages it for user input:

Rendering arbitrary HTML dynamically on your site can pose significant risks, leading to XSS vulnerabilities. Utilize HTML interpolation solely for trusted content and never for user-supplied content.

Instead, opt for string interpolation in this case:

Vue.component('reverse', {
  // ...
  //template: '<p v-html="reverseMessage(msgreverse)"></p>'  // AVOID THIS
  template: '<p>{{reverseMessage(msgreverse)}}</p>'
})

Vue.component('reverse', {
  props: ['msgreverse'],
  methods: {
    reverseMessage(msg) {
      return msg.split('').reverse().join('')
    }
  },
  template: '<p>{{reverseMessage(msgreverse)}}</p>'
})

new Vue({
  el: '#app',
  data: () => ({
    message: 'Hello Vue.js!',
  }),
})

<script src="https://unpkg.com/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="96e0e3c6fbb9a7bc51afb2" rel="noopener noreferrer">[email protected]</a>"></script>

<div id="app">
  <reverse :msgreverse="message"></reverse>
</div>

Answer 2

The issue at hand is that Vue is not recognizing the global function you have created (i.e., reverseMessage()). Vue does not have visibility over global functions or variables during template rendering. Local functions, on the other hand, can be accessed within the component's methods property. In your scenario, it should be structured like this:

Vue.component('reverse', {
  // ...
  methods: {
    reverseMessage(msg) {
      return msg.split('').reverse().join('')
    }
  }
})

Given that the component is intended for string reversal, there is no necessity for a prop to be allocated for the reverseMessage function. Thus, you can eliminate it from props:

Vue.component('reverse', {
  // ...
  //props:["msgreverse", "reverseMessage"],  // AVOID THIS
  props:["msgreverse"],
})

Your template is employing the v-html directive to display the reversed message, but this is unnecessary because (1) the message itself is not in HTML format, and (2) Vue discourages it for user input:

Rendering arbitrary HTML dynamically on your site can pose significant risks, leading to XSS vulnerabilities. Utilize HTML interpolation solely for trusted content and never for user-supplied content.

Instead, opt for string interpolation in this case:

Vue.component('reverse', {
  // ...
  //template: '<p v-html="reverseMessage(msgreverse)"></p>'  // AVOID THIS
  template: '<p>{{reverseMessage(msgreverse)}}</p>'
})

Vue.component('reverse', {
  props: ['msgreverse'],
  methods: {
    reverseMessage(msg) {
      return msg.split('').reverse().join('')
    }
  },
  template: '<p>{{reverseMessage(msgreverse)}}</p>'
})

new Vue({
  el: '#app',
  data: () => ({
    message: 'Hello Vue.js!',
  }),
})

<script src="https://unpkg.com/<a href="/cdn-cgi/l/email-protection" class="__cf_email__" data-cfemail="96e0e3c6fbb9a7bc51afb2" rel="noopener noreferrer">[email protected]</a>"></script>

<div id="app">
  <reverse :msgreverse="message"></reverse>
</div>

Answer 3

Answer №2

Although my response may not directly address the previous question, it does pertain to a common Google search query regarding

Vue.JS "TypeError: <functionName> is not a function"

Oops, looks like I made a simple mistake...

In my case, I had multiple methods objects defined in a lengthy file, causing the second one to inadvertently override the first.

methods: {
  importantFunctionThatIsNotWork: () => {}
}, 

... // Numerous lines of code in a file where collisions aren't immediately visible in my IDE

methods: {
  allMyOtherFunctions: () => {}
  // ...
},

...So, I combined the two like this

methods: {
  importantFunctionThatIsNotWork: () => {},
  allMyOtherFunctions: () => {}
  // ...
},

Answer 4

Although my response may not directly address the previous question, it does pertain to a common Google search query regarding

Vue.JS "TypeError: <functionName> is not a function"

Oops, looks like I made a simple mistake...

In my case, I had multiple methods objects defined in a lengthy file, causing the second one to inadvertently override the first.

methods: {
  importantFunctionThatIsNotWork: () => {}
}, 

... // Numerous lines of code in a file where collisions aren't immediately visible in my IDE

methods: {
  allMyOtherFunctions: () => {}
  // ...
},

...So, I combined the two like this

methods: {
  importantFunctionThatIsNotWork: () => {},
  allMyOtherFunctions: () => {}
  // ...
},

The error message "reverseMessage is not a function" occurred in Vue.JS

Answer №1

Answer №2

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