Js why use var

This means that if a function uses the same variable, the "var" variable you declared will overwrite the non-var variable in your function JavaScript Scopes. It always worth to use a var if you are defining new variable. How are we doing? Please help us improve Stack Overflow. Take our short survey. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow.

Learn more. When to use var in Javascript [duplicate] Ask Question. Asked 10 years, 7 months ago. Active 4 years, 1 month ago. Viewed 38k times. Improve this question. OscarRyz OscarRyz k gold badges silver badges bronze badges. Add a comment. In order to fully understand the differences between each of the identifiers we first need to understand the concept of scope.

Scope determines the accessibility or visibility of variables to JavaScript. There are three types of scope in JavaScript:. Global scope. Function local scope. Block scope new with ES6. Variables declared outside a function are in the global scope. Global variables can be accessed and changed in any other scope. Variables defined within a function are in local scope and are not accessible in other functions.

Each function, when invoked, creates a new scope, therefore variables with the same name can be used in different functions. Variables declared inside a block scope will remain in the scope they were already in. Before ES6, the var keyword was used to declare a variable in JavaScript. Variables declared using the var keyword are either globally or functionally scoped, they do not support block-level scope.

This means that if a variable is defined in a loop or in an if statement it can be accessed outside the block and accidentally redefined leading to a buggy program. As a general rule, you should avoid using the var keyword. In many ways, the let keyword is very similar to the var keyword as they both allow you to reassign the value later on. When we have a closure with a var variable, the reference is remembered, which can be troublesome when inside a loop where that variable changes.

Using let , a new reference is created each time. Do you still find yourself using var? Share your experiences below! Coding tutorials and news. The developer homepage gitconnected. Sign in. Jonathan Hsu Follow. Level Up Coding Coding tutorials and news.

Thanks to Zack Shapiro. Top writer with 2. Level Up Coding Follow. Written by Jonathan Hsu Follow. More From Medium. The Node. RisingStack in Node.