Something seems to be missing in Vue.js as it cannot compute the property 'length' of null

Question

Something seems to be missing in Vue.js as it cannot compute the property 'length' of null

When I attempt the following:

<div class="panel panel-default" v-if="socialiteLogins !== null">

The panel remains visible. Checking socialiteLogins === null or with == both indicate that the object is not null, even though it actually is. When dumped on the page, it returns [] as the result - an empty JSON object. Thus, trying this results in the same issue:

<div class="panel panel-default" v-if="socialiteLogins.length !== 0">

The panel still does not hide and triggers the error message:

Cannot read property 'length' of null

However, if I use the following condition:

<div class="panel panel-default" v-if="socialiteLogins !== null && socialiteLogins.length !== 0">

It successfully hides the panel without any warnings upon initial load. Yet, updating the socialiteLogins variable later may trigger the length warning when it reverts back to an empty JSON object. Any thoughts on why this occurs?

Edit:

Expanding on this... if I try:

<div class="panel panel-default" v-show="socialiteLogins">

The panel appears on initial load even when there are no records present. However, removing them after the page loads correctly hides the panel. It seems the only issue lies during the initial loading phase, where it fails to detect the absence of records.

javascript vue.js

Answer 1

Answer №1

While my expertise lies more in general JavaScript, the principles discussed here can be applied to Vue.js as well.

If the variable socialiteLogins is either null or undefined, attempting to access its length property will result in an error. This property can only be accessed if socialiteLogins is of type array, object, or function. This explains why you are seeing the message:

Cannot read property 'length' of null

Even if socialiteLogins is empty (or explicitly set to undefined), it is not equivalent to being null. It's essential to note this distinction, especially when using a loose comparison like == null.

In cases where socialiteLogins is an empty array, it is still considered truthy by JavaScript. Consequently, the v-show directive will interpret it as true, leading to unexpected behavior in your code.

The root cause of the issue you're facing stems from these underlying facts.

To address this problem effectively, consider modifying your code snippet as follows:

<div class="panel panel-default" v-show="socialiteLogins && socialiteLogins.length">

Here's how it works:

The && operator in JavaScript checks the validity of the first statement. If it evaluates to true, it proceeds to evaluate the second statement. Otherwise, it returns the initial value encountered.

When used with the v-show directive, this expression undergoes a boolean coercion process.

If socialiteLogins is either undefined or null, the operator returns that specific value, which then gets coerced into false.

In cases where socialiteLogins represents an empty array, it is still considered a truthy value. As such, the && operator evaluates the next condition (socialiteLogins.length), resulting in 0 and subsequently being coerced to false.

For non-empty arrays, the truthiness of socialiteLogins ensures the evaluation of socialiteLogins.length, yielding a non-zero value that translates to true.

Answer 2

While my expertise lies more in general JavaScript, the principles discussed here can be applied to Vue.js as well.

If the variable socialiteLogins is either null or undefined, attempting to access its length property will result in an error. This property can only be accessed if socialiteLogins is of type array, object, or function. This explains why you are seeing the message:

Cannot read property 'length' of null

Even if socialiteLogins is empty (or explicitly set to undefined), it is not equivalent to being null. It's essential to note this distinction, especially when using a loose comparison like == null.

In cases where socialiteLogins is an empty array, it is still considered truthy by JavaScript. Consequently, the v-show directive will interpret it as true, leading to unexpected behavior in your code.

The root cause of the issue you're facing stems from these underlying facts.

To address this problem effectively, consider modifying your code snippet as follows:

<div class="panel panel-default" v-show="socialiteLogins && socialiteLogins.length">

Here's how it works:

The && operator in JavaScript checks the validity of the first statement. If it evaluates to true, it proceeds to evaluate the second statement. Otherwise, it returns the initial value encountered.

When used with the v-show directive, this expression undergoes a boolean coercion process.

If socialiteLogins is either undefined or null, the operator returns that specific value, which then gets coerced into false.

In cases where socialiteLogins represents an empty array, it is still considered a truthy value. As such, the && operator evaluates the next condition (socialiteLogins.length), resulting in 0 and subsequently being coerced to false.

For non-empty arrays, the truthiness of socialiteLogins ensures the evaluation of socialiteLogins.length, yielding a non-zero value that translates to true.

Answer 3

Answer №2

Big thanks to @RyanZim for the helpful answer. For anyone stumbling upon this in their future searches, here's the solution that worked:

The issue stemmed from the initial state of the data. In my case, it looked like this:

data: function() {
    return {
        socialiteLogins: null
    }
},

This setup worked fine for checking !== null but ran into problems when trying to check .length. The key is to maintain the proper type throughout so a consistent check can be performed:

data: function() {
    return {
        socialiteLogins: []
    }
},

Answer 4

Big thanks to @RyanZim for the helpful answer. For anyone stumbling upon this in their future searches, here's the solution that worked:

The issue stemmed from the initial state of the data. In my case, it looked like this:

data: function() {
    return {
        socialiteLogins: null
    }
},

This setup worked fine for checking !== null but ran into problems when trying to check .length. The key is to maintain the proper type throughout so a consistent check can be performed:

data: function() {
    return {
        socialiteLogins: []
    }
},

Answer 5

Answer №3

Receive this helpful suggestion:

<div class="panel panel-default" v-if="Object.keys(socialiteLogins).length > 0">

That's all there is to it.

Flag as resolved.

Answer 6

Receive this helpful suggestion:

<div class="panel panel-default" v-if="Object.keys(socialiteLogins).length > 0">

That's all there is to it.

Flag as resolved.

Something seems to be missing in Vue.js as it cannot compute the property 'length' of null

Answer №1

Answer №2

Answer №3

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