Introduction to Javascript method of converting variables into strings

This article mainly introduces you to three methods of converting variables into strings in Javascript. These three methods are: value.toString(), "" + value and String(value). The article passes The sample code is introduced in very detail. Friends who need it can follow the editor to learn together.

Preface

Everyone should know that for JavaScript, there are 3 different ways to convert variables into strings. This article will introduce these methods in detail and compare their advantages and disadvantages. Not much to say below, let’s take a look at the detailed introduction.

3 methods

The 3 methods to convert a variable into a string are as follows:

• value. toString()

• ##"" + value

• ##String(value)

When value is null or undefined, the first method will not work. And method 2 and method 3 are basically the same.

Add value to an empty string to convert it to a string. This method is actually a slightly obscure technique that may make it difficult for others to understand the developer's intentions. However, this is a matter of opinion, and some people prefer this method. String(value): This method is very clear: use the

function to convert value to a string. However, String() has two different uses, which is easy to confuse, especially for Java developers. When String() is used as a constructor together with operator new, it returns a newly created String object; when String() is called without new operator, it only value is converted into a raw string. The two are very different:

> String("Fundebug") === new String("Fundebug")
false
> typeof String("Fundebug")
'string'
> String("Fundebug") instanceof String
false
> typeof new String("Fundebug")
'object'
> new String("Fundebug") instanceof String
true

as a constructor, so use it only Just convert the string.

""+Subtle differences between value and String(value)

and String(value) can convert value into a string. How do they do it? In fact, although their results are the same, their methods are slightly different.

Convert the primitive basic type to a stringBoth methods use the internal function

Convert the primitive Basic types are converted to strings. ToString()The function is defined in ECMAScript 5.1 (§9.8), but cannot be used directly, so it is called an internal function. The following table shows how the ToString() function converts primitive primitive types to strings:

var obj = {
 valueOf: function()
 {
  console.log("valueOf");
  return {};
 },
 toString: function()
 {
  console.log("toString");
  return {};
 }
};

> "" + obj
valueOf
toString
TypeError: Cannot convert object to primitive value
> String(obj)
toString
valueOf
TypeError: Cannot convert object to primitive value

> var x = {}
> x.valueOf() === x
true