This content originally appeared on DEV Community and was authored by Paul Thompson
The var keyword was JavaScript's first way to declare a variable. It fits, right? Var, variable, it's in the name. But like the Joker, var is more than pretty face -- it has some baggage. As a beginning programmer, or a seasoned one dipping your toe into the seedy underbelly of JavaScript development, you maybe be wondering when you should use var to declare your JavaScript objects and functions.
Never fear. I have 3 reasons for you to use var in your next JavaScript project.
You love tradition and spurn anything new
Var maybe the oldest keyword to declare a variable, but it is by far the only one. It's younger cousins, let and const exploded onto the scene with ES6 (over 6 years ago as of this writing!). But if sticking to old norms fraught with perils is your thing, keep using var and leave these upstart keywords to listen to their terrible pop music and complain about their parents.
You prefer mutability, even when you don't
Var has the troubling distinction of creating a variable of any type, which can then be changed to a variable of any type later. That's right, the number you declared on line 4 just became a string on line 17 and a boolean on line 109. This type flexibility is a key feature of JavaScript, but it can be avoided. But if you too like to live dangerously, keep using var.
You like leaky scopes
Prior to ES6, JavaScript variables were always defined at the function scope. In a lot of cases, this meant variables were global. JavaScript didn't enforce block-level scopes such as inside a for loop or if block. So a variable declared with var would be hoisted to the top of its function scope. In other words, the variable declaration moved to the top of the current lexical environment with a value of undefined. A common issue arising from hoisting is that such variables are accessible outside the block scope, where the developer may not expect them to be.
A subtler and more difficult to detect bug can happen here as well, variable shadowing. Rarely this may be desired. If that is you, var is your hero.
There must be a better way
If you made it this far, you're probably seconds away from pounding out a fierce comment about how I'm wrong about var. The truth is, no one should be using var in any JavaScript code except for a history lesson. Even then, it should come with a footnote that says something like, "please don't ever do this."
Let and const have been available in every major browser for the last 6 years. This is really, really ancient in frontend years. var isn't just the parent misunderstanding their teen, it's the great grandparent everyone loves but no one invites to the fun parties.
Let retains JavaScript's flexible type system while enabling block-scoping. Const creates a -- you guessed it -- constant variable in block-scope. Const creates a that cannot be reassigned, but similar to most other languages, const objects can have their properties mutated. These two alternatives to var should cover every use case you have. Even if you are in the tough spot of needing to support truly archaic browsers, don't use var. Use a tool such as Babel.
So please, please, do not use var.
This content originally appeared on DEV Community and was authored by Paul Thompson
Paul Thompson | Sciencx (2021-11-08T22:19:53+00:00) 3 reasons to use ‘var’ in JavaScript. Retrieved from https://www.scien.cx/2021/11/08/3-reasons-to-use-var-in-javascript/
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