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This article introduces the relevant knowledge of "how to judge whether a variable is a string or not". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Judgment method: 1, use "typeof variable = 'string'" statement; 2, use "variable instanceof String"; 3, use "Object.prototype.toString.call (variable) = =" [object String] "".

The operating environment of this tutorial: windows7 system, javascript1.8.5 version, Dell G3 computer.

Es6 determines whether a variable is a string

Method 1: use the typeof keyword

The grammar rule of typeof is: typeof operand.

We can directly use typeof a = = 'string' to determine, and if the return value is true, it is a string.

Example:

Var a = "123456"; typeof a = = 'string';var baked 123456 bordering typeof b = =' string'

In addition, list a few special cases of this operator:

Typeof Null; / / 'object'typeof NaN; / /' number'typeof Array; / / 'object'

Method 2: use the instanceof keyword

The syntax rule of instanceof is object instanceof constructor. The return value is of type boolean.

Instanceof works to see if the prototype property of the constructor exists on the prototype chain of the object. This means that it can only judge the type of object.

If we use new String ("I am string") to construct a string, we can also use instanceof to determine. As follows:

New String ("I am string") instanceof String

Method 3:Object.prototype.toString.call ()

This method returns "[object type]" by default, where type is the data type. It's worth noting that we have to use call when we call it.

Var a = "123456"; Object.prototype.toString.call (a) = "[object String]"; var baked 123456 / Object.prototype.toString.call (b) = = "[object String]"

This is the end of "how es6 determines whether a variable is a string". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

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