Using the let statement, you can create Block scoped local variables in JavaScript. The let statement was introduced in the ECMAScript 6 standard of JavaScript.

Before ECMAScript 6, JavaScript had three types of scoping:

  • Global scoping
  • Functional scoping
  • Lexical scoping

To explore let statement in detail, consider the code snippet given below:

You will get this output for the above code listing:

image

In the above listing, variable x is declared using the var statement. Hence, the scope of variable x is a function scope. Variable x inside the if statemnet is same variable x which was created outside the if statement. So, when you modify the value of variable x inside the if statement block, it modifies the value for all references of variable x in the function.

To avoid this, you need block-level scoping, and the let statement allows you to create a block-scoped local variable.

Let’s modify the above code snippet and use the let statement to declare the variable:

In the above code snippet, you are declaring scope level local variable x using the let statement. Therefore updating value of variable x inside the if statement will not affect value of variable x outside the if statement.

Read full article on the Infragistics blog

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