CODEWITHSUNDEEP
javascript
user6329530
user6329530

Reputation:

Can not assign variable because type is null?

canvas.getActiveObject().type returns the type of the currently active element in the canvas.

var type = canvas.getActiveObject().type;
if(type){
     console.log(type);
}

But when no element is active, I get TypeError, which of course happens because no element is active so there is nothing to getActiveObject from.

TypeError: canvas.getActiveObject(...) is null

Why can't I assign a variable when the activeObject is null?

Same error happens, when I try 

var type = '';
if(canvas.getActiveObject().type){
    type = canvas.getActiveObject().type
}

Upvotes: 1

Views: 67

Answers (3)

Andrew Shepherd
Andrew Shepherd

Reputation: 45252

canvas.getActiveObject() is returning null.

That means that canvas.getActiveObject().type is the same as null.type.

Referencing any member of null will throw an exception.

You can solve this any number of ways

Three lines of code:

let type = '';
if(canvas.getActiveObject()) {
    type = canvas.getActiveObject().type;
}

Or a one-liner:

let type = canvas.getActiveObject()
   ? canvas.getActiveObject().type
   : '';

Or a more compact one-liner:

let type = (canvas.getActiveObject() || { type: ''}).type;

Upvotes: 2

MellowArpeggiation
MellowArpeggiation

Reputation: 41

It looks like you're trying to access the property type returned by the function getActiveObject(), but since the function returns null, accessing the type property is throwing an error. What you need to do instead is check the return value of getActiveObject() before trying to access any of its members.

The snippet below, which is based on your code, instead checks that the active object returned is not null before attempting to access the members that reside within it.

var activeObject = canvas.getActiveObject();
if (activeObject) {
     console.log(activeObject.type);
}

Upvotes: 1

Louay Al-osh
Louay Al-osh

Reputation: 3405

You can't access a null value like an object, I think you should safely access the value like.

var type = '';
if(canvas.getActiveObject() && canvas.getActiveObject().type){
    type = canvas.getActiveObject().type
}

Upvotes: 2

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