Does javascript need to declare variables?

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1. In strict mode, variables must be declared before they can be used.

2. In non-strict mode, JavaScript allows you to assign values to variables without declaring them, because the JavaScript interpreter can automatically implicitly declare variables.

Implicitly declared variables are always used as global variables.

Declare variable

In JavaScript, var statements are used to declare variables.

Example

In a var statement, one or more variables can be declared or assigned, and unassigned variables are initialized to undefined (undefined) values. When declaring multiple variables, you should use comma operators to separate them.

Var a; / declare a variable var aMagne bjournal; / / declare multiple variables var b = 1; / / declare and assign [xss_clean] (a); / / return undefined [XSS _ clean] (b); / / return 1 Thank you for reading! This is the end of the article on "does javascript need to declare variables?". I hope the above content can be of some help to you, so that you can learn more knowledge. if you think the article is good, you can share it for more people to see!