Is it advisable to set default values for variables upon initialization in JavaScript?

I am currently working with an AngularJS controller and I am following the guidelines set by John Papa when it comes to binding variables at the top. My question is: does initializing variables with default values during declaration offer any performance advantages, or does it have a negative impact on performance?

function someCtrl($scope) {
    var vm = this;
    vm.someVar = '';    // Should it rather be vm.someVar; ?
}

While my question pertains to AngularJS, it can also be considered as a general JavaScript query.

UPDATE: In another scenario, what if we do the following:

function someCtrl($scope) {
    var someVar = '';    // Should it rather be var someVar; ?
}

Answer №1

vm.someVar = ''; - Would it be more appropriate to use vm.someVar; instead?

This is not just a variable or a declaration.

It's actually an assignment that generates a property on the vm object. On the other hand, vm.someVar; is simply a no-op (it doesn't do anything) and can be omitted entirely.

Indeed, if you intend to create properties, it is essential to initialize them. You could start by setting them to undefined, but it's preferable to provide an initial value of the same type they will eventually have. Furthermore, it is recommended to define properties in the constructor (when creating the object) rather than adding them later.

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