What are the reserved words that are not JavaScript?

JavaScript is a very popular programming language and is widely used in web development, game development, mobile application development and other fields. When using JavaScript, we need to know some reserved words, such as if, else, for, while, etc. These reserved words have specific meanings and usages and are an integral part of JavaScript. However, in addition to these reserved words, JavaScript has many other words and symbols that are not reserved words in JavaScript, but also play an important role in programming.

First, let’s look at some words that are not JavaScript reserved words. One of them is NaN, which stands for "Not-a-Number" and indicates a value that is not a number. NaN is mainly used to check whether the value is legal. When we try to perform illegal mathematical operations, such as multiplying strings and numbers, JavaScript will return NaN.

There is also a non-reserved word undefined, which represents an undefined value. In JavaScript, if a variable is not assigned a value, its value is undefined. We can also set the value of a variable to undefined, so that it becomes an undefined value.

Another word that is not a reserved word is null. It represents an empty value, used to indicate that a variable should have a value, but currently no value is available.

In addition to these words, JavaScript also has some symbols that are not reserved words, but they also play an important role. For example, the double question mark (??) is a logical operator used to determine whether a variable is null or undefined. Three dots (...) represent expansion syntax, which can expand an array or object into multiple parameters or elements. Square brackets ([]) and curly brackets ({}) are symbols used to represent arrays and objects respectively.

In addition, JavaScript has some other symbols. Although they are not reserved words, they are very useful in actual programming. For example, colon (:) is used to define the name and value of a label or object attribute, semicolon (;) is used to indicate the end of a statement, and comma (,) is used to separate elements or attributes in an array or object. Although these symbols look simple, they greatly enrich the programming capabilities of JavaScript.

When writing JavaScript programs, we need to keep in mind the usage and meaning of JavaScript reserved words, but at the same time, we must also learn to use other words and symbols to achieve richer functions. These non-reserved words and symbols are equally important in actual programming. They can help us better implement the functions we need and improve our programming efficiency.

In short, in addition to common reserved words, JavaScript has many other words and symbols, which are equally important and require us to apply them in actual programming. By learning and mastering these non-reserved words and symbols, we can better realize the various functions of JavaScript programs and improve our programming skills.

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