Grammar rules for declaring variable names in JavaScript_javascript tips

1. Grammar rules

　1. Variables must start with a letter, underscore (_) or dollar sign ($).

　2. Then you can use any number of English letters, numbers, underscores (_) or dollar signs ($).

　3. JS keywords and reserved words cannot be used.

2. Examples

　　var score;
　　score="100";

3. Attention

　1.JS is case-sensitive. For example, the variables score and Score are different and equivalent to two variables.

　2. Although variables can be used directly without declaring them, they are not standardized and may involve issues such as variable name promotion.

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