Quick Answer: Should You Use VAR Or Let?

Is let faster than VAR?

After testing this in Chrome and Firefox, this shows that let is faster than var , but only when inside a different scope than the main scope of a function.

In the main scope, var and let are roughly identical in performance.

In IE11 and MS Edge, let and var are roughly equal in performance in both cases..

Is var a bad practice?

var speeds up the writing, but may slow down the reading a bit. It’s obviously not a code behaviour rule like “Always initialize variables” because the two alternatives (writing var and writing the type) have exactly the same behaviour. So it’s not a critical rule.

Should I use VAR or let JavaScript?

Use let as a general rule, and var on occasion. Block scoping is the standard and most readable choice, and will make debugging easier. … Function scoping makes things a lot less apparent, and much easier to accidentally introduce bugs with scoping mistakes. In general, the smaller the scope you can use, the better.

Is Const better than let?

Turns out, const is almost exactly the same as let . However, the only difference is that once you’ve assigned a value to a variable using const , you can’t reassign it to a new value. … The take away above is that variables declared with let can be re-assigned, but variables declared with const can’t be.

Is Let hoisted?

All declarations (function, var, let, const and class) are hoisted in JavaScript, while the var declarations are initialized with undefined , but let and const declarations remain uninitialized. They will only get initialized when their lexical binding (assignment) is evaluated during runtime by the JavaScript engine.

Should you still use VAR?

Variables declared with var are not block scoped (although they are function scoped), while with let and const they are. This is important because what’s the point of block scoping if you’re not going to use it.

Why you should not use VAR?

In Javascript, it doesn’t matter how many times you use the keyword “var”. If it’s the same name in the same function, you are pointing to the same variable. … They both work with block scope, which means, if variables or constants are declared inside a block, they will not be available to the “parent” blocks.

What’s the difference between VAR and let?

The main difference between let and var is that scope of a variable defined with let is limited to the block in which it is declared while variable declared with var has the global scope. So we can say that var is rather a keyword which defines a variable globally regardless of block scope.

Why is var better than let?

let allows you to declare variables that are limited in scope to the block, statement, or expression on which it is used. This is unlike the var keyword, which defines a variable globally, or locally to an entire function regardless of block scope.

Does IE support let?

Internet Explorer browser version 11 partially supports JAVASCRIPT let and partial support for Internet Explorer refers ot supporting an older version of the web browser.

What is the difference between const and let and VAR?

var declarations are globally scoped or function scoped while let and const are block scoped. var variables can be updated and re-declared within its scope; let variables can be updated but not re-declared; const variables can neither be updated nor re-declared. They are all hoisted to the top of their scope.

When should you use var to declare a variable over Let?

var is used to declare a variable value – you could change its value as you wish. One more difference, which I’ve encountered in other languages for Constants is : can’t initialise the constant(let) for later , should initialise as you’re about to declare the constant.

Is VAR needed JavaScript?

2 Answers. The var keyword is never “needed”. However if you don’t use it then the variable that you are declaring will be exposed in the global scope (i.e. as a property on the window object). … Usually you only want your variable to be visible in the current scope, and this is what var does for you.

What is the purpose of using VAR?

Using var lets you hide external variables that have the same name. In this way you can simulate a “private” variable, but that’s another topic. A rule of thumb is to always use var , because otherwise you run the risk of introducing subtle bugs.

Why VAR is used in JavaScript?

JavaScript uses reserved keyword var to declare a variable. A variable must have a unique name. … We have assigned values to variables one and two at the same time when we declared it, whereas variable three is declared but does not hold any value yet, so it’s value will be ‘undefined’.

Is VAR deprecated in JavaScript?

The scope of a JavaScript variable declared with var is its current execution context. … The let statement allows you to create a variable with the scope limited to the block on which it is used. const. const statement values can be assigned once and they cannot be reassigned.

Is JavaScript hoisting bad?

Variables declared using var can be accessed in the whole scope (and we already know that var has a bigger scope). You can access them before they are declared. In such case, their value would be undefined though, as only declarations and not initializations are hoisted. This is generally considered a bad practice.

What is the proper way to declare a variable?

To declare (create) a variable, you will specify the type, leave at least one space, then the name for the variable and end the line with a semicolon ( ; ). Java uses the keyword int for integer, double for a floating point number (a double precision number), and boolean for a Boolean value (true or false).

What is == and === in JavaScript?

== in JavaScript is used for comparing two variables, but it ignores the datatype of variable. === is used for comparing two variables, but this operator also checks datatype and compares two values. … It returns true only if both values and data types are the same for the two variables.

Can var be Redeclared?

var was the way to declare variables before ES6. It can be redeclared and reassigned.

What is var keyword in Java?

In Java 10, the var keyword allows local variable type inference, which means the type for the local variable will be inferred by the compiler, so you don’t need to declare that. … Each statement containing the var keyword has a static type which is the declared type of value.