What are the situations where JavaScript variable names are illegal?

JavaScript is a programming language widely used in web pages and browsers. We can use it to enhance the interactivity and dynamics of web pages. In JavaScript, variables are a very important concept that can be used to store and manipulate data. However, variable names have their own rules and restrictions in JavaScript. In this article, we will discuss the situations in which JavaScript variable names are illegal.

In JavaScript, variable names must start with a letter, underscore, or dollar sign. Variable names can contain letters, numbers, underscores, or dollar signs, but they cannot contain spaces and other special characters. There is no limit on the length of variable names, but it is best not to be too long to keep the code readable.

Let’s look at some situations where variable names are illegal:

1. Variable names cannot start with a number.

JavaScript variable names cannot start with a number. This is because JavaScript treats variable names that start with a number as a numeric type. For example, the variable name 123 would be interpreted as the number 123, not as a variable name. Therefore, if you want to use a number as part of a variable name, you should precede the variable name with a letter or an underscore.

2. Variable names cannot contain spaces or other special characters.

In JavaScript, variable names cannot contain special characters such as spaces, periods, " ", and "-". These characters will be interpreted by JavaScript as part of the code, not part of the variable name. If you want to represent a variable name with multiple words, you can use camelCase, such as myVariableName.

3. Variable names cannot be the same as JavaScript keywords.

In JavaScript, some keywords are reserved and cannot be used as variable names. These keywords include if, else, for, while, function, etc. If you use these keywords as variable names, it will cause a syntax error.

4. The variable name cannot be the same as the JavaScript built-in object or function name.

In JavaScript, there are many built-in objects and functions, such as Math, Number, Array, etc. If your variable names match the names of these objects or functions, it will cause errors in your code. The best way to avoid this is to use meaningful, clear variable names.

5. Variable names cannot contain special symbols.

In JavaScript, variable names cannot contain special symbols, such as "@", "#", "$", etc. These symbols are considered syntax errors, so we should not use them as variable names.

6. Variable names cannot begin with a hyphen.

In JavaScript, variable names cannot start with a hyphen ("-"). This is because JavaScript interprets the hyphen as a minus sign and not as part of the variable name. If you want to use a hyphen as part of a variable name, use an underscore instead.

In short, the legality of JavaScript variable names plays a very important role in the writing and execution of code. If your variable name is illegal, the code will not be interpreted or run correctly. Therefore, we should follow JavaScript variable naming rules and choose variable names carefully to ensure the correctness and readability of the code.

The above is the detailed content of What are the situations where JavaScript variable names are illegal?. For more information, please follow other related articles on the PHP Chinese website!