Why Is Let Better Than VAR?

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 happens if you dont use VAR in JavaScript?

If you don’t use var , the variable bubbles up through the layers of scope until it encounters a variable by the given name or the global object (window, if you are doing it in the browser), where it then attaches. … If you use var in the global scope, the variable is truly global and cannot be deleted.

Is Let better than VAR?

The let and const declarations provide better scope management than the traditional var. Plus the var keyword may confuse programmers coming from other languages like VB or Java that use var to declare variables, but with different rules.

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 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.

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.

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 const?

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. … While var and let can be declared without being initialized, const must be initialized during declaration.

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 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.

What can I use instead of VAR in JavaScript?

Use ‘let’ and ‘const’ instead of ‘var’var uses something called ‘hoisting’, which can lead to unexpected results.let and const are both block-scoped. Which means you can declare them in for loop or if statement, and they will only be valid for that block. This helps with spotting bugs and makes your code more robust.const prevents variable re-assignment.Aug 29, 2018

What is the most significant difference between Let & VAR?

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.

Should you ever use VAR in JavaScript?

Most Javascript experts agree var shouldn’t be used. Douglas Crockford, the man who popularized JSON, is against the use of var. He indicates that, “var might possibly still be useful in an extreme case like machine-generated code, but I’m stretching hard there.