An in-depth analysis of JavaScript string operation methods slice, substr, substring and their IE compatibility_javascript skills

The substr(), substring(), and slice() methods are often used when intercepting strings. Sometimes the usages are confused, so I will summarize them.

Reading Directory
•slice()
•substring()
•substr()
•Summary

slice()

Definition: Accepts one or two parameters, the first parameter specifies the starting position of the substring. The second parameter represents the end position of the substring (excluding the character at the end position). If the second parameter is not passed, the length of the string is used as the end position.

1. When the passed parameter is a positive value:

var str ="helloWorld";
// 一个参数，则将字符串长度作为结束位置
alert(str.slice(3)); // "loWorld"
// 两个参数，7位置上的字符为"r",但不包括结束位置的字符
alert(str.slice(3,7)); // "loWo" 

2. When the passed parameter is a negative value:

slice()方法会将传入的负值与字符串长度相加。
 var str ="helloWorld";
// 一个参数，与字符串长度相加即为slice(7)
alert(str.slice(-3)); // "rld"
// 两个参数，与字符串长度相加即为slice(3,6)
alert(str.slice(3,-4)); // "loW" 

3. When the second parameter is smaller than the first parameter:

If the second parameter passed in by the slice() method is smaller than the first parameter, an empty string will be returned.

var str ="helloWorld";
alert(str.slice(5,3)); // "" 

4. IE compatibility

When tested with IE8 browser, there is no problem and the behavior is consistent with modern browsers.

substring()

Definition: Accepts one or two parameters, the first parameter specifies the starting position of the substring. The second parameter represents the end position of the substring (excluding the character at the end position). If the second parameter is not passed, the length of the string is used as the end position.

1. When the passed parameter is a positive value: the same behavior as the slice() method

var str ="helloWorld";
// 一个参数，则将字符串长度作为结束位置
alert(str.substring(3)); // "loWorld"
// 两个参数，7位置上的字符为"r",但不包括结束位置的字符
alert(str.substring(3,7)); // "loWo" 

2. When the passed parameter is a negative value:

The substring() method will convert all negative parameters to 0. Let’s take a look at an example:

var str ="helloWorld";
// 两个参数，-4会转换为0，相当于substring(3,0) -->即为 substring(0,3)
alert(str.substring(3,-4)); // "hel" 

The

substring() method will use the smaller number as the starting position and the larger number as the ending position. As in the above example, substring(3,0) and substring(0,3) have the same effect.

4. IE compatibility

When tested with IE8 browser, there is no problem and the behavior is consistent with modern browsers.

substr()

Definition: Accepts one or two parameters, the first parameter specifies the starting position of the substring. The second parameter is somewhat different from the previous method, indicating the number of characters returned. If no second argument is passed, the length of the string is used as the ending position. Let’s see an example:

1. When the passed parameter is a positive value:

var str ="helloWorld";
// 一个参数，则将字符串长度作为结束位置
alert(str.substr(3)); // "loWorld"
// 两个参数，从位置3开始截取后面7个字符
alert(str.substr(3,7)); // "loWorld" 

2. When the passed parameter is a negative value:

The

substr() method adds the negative first parameter to the length of the string and converts the negative second parameter to 0.

var str ="helloWorld";
// 将第一个负的参数加上字符串的长度--->
//即为：substr(7,5) ，从位置7开始向后截取5个字符
alert(str.substr(-3,5)); // "rld"
// 将第二个参数转换为0
// 即为：substr(3,0)，即从位置3截取0个字符串，则返回空
alert(str.substr(3,-2)); // "" 

3. IE compatibility

The substr() method will have problems when passing negative values, and the original string will be returned. IE9 fixes this issue.

Summary

The behavior of slice() and substring () is consistent when passing positive parameters, and the substr() method will be easily confused on the second parameter

When passing negative parameters, the slice() method is to add the length of the string, which is in line with general thinking. Converting the second parameter of substring() to 0 will easily cause problems, and the starting position will be easy to change. substr () method will cause IE compatibility problems when it has a negative value.

To sum up, I generally recommend using the slice() method.

Let me introduce to you the differences between slice, substr and substring

First of all, they both receive two parameters. slice and substring receive the starting position and the end position (excluding the end position), while substr receives the starting position and the length of the string to be returned. Just look at the example below:

 var test = 'hello world';
  alert(test.slice(,));    //o w
  alert(test.substring(,));   //o w
  alert(test.substr(,));   //o world 

One thing to note here is that substring uses the smaller of the two parameters as the starting position, and the larger parameter as the ending position.

For example:

alert(test.substring(7,4));   //o w 

Next, when the received parameter is a negative number, slice will add the length of its string to the corresponding negative number, and the result will be used as the parameter; substr will only be the result of adding the first parameter and the length of the string. As the first parameter; substring simply converts all negative parameters directly to 0. The test code is as follows:

var test = 'hello world';  
alert(test.slice(-));   //rld  
alert(test.substring(-));  //hello world  
alert(test.substr(-));  //rld  
alert(test.slice(,-));  //lo w  
alert(test.substring(,-)); //hel  
alert(test.substr(,-));  //空字符串 

Note: IE has an error in handling negative values ​​received by substr, and it will return the original string.