Advanced JavaScript (7) The difference between JS interception string substr and substring methods

The difference between JS intercepting string substr and substring methods

substr method

Returns a substring of the specified length starting from the specified position.

stringvar.substr(start [, length ])

Parameters

stringvar

Required. The string literal or String object from which the substring is to be extracted.

start

Required option. The starting position of the desired substring. The first character in the string has index 0.

length

Optional. The number of characters that should be included in the returned substring.

Description

If length is 0 or a negative number, an empty string will be returned. If this parameter is not specified, the substring will be continued to the end of stringvar.

Example

The following example demonstrates the use of the substr method.

function SubstrDemo(){
   var s, ss;                // 声明变量。
   var s = "The rain in Spain falls mainly in the plain.";
   ss = s.substr(12, 5);     // 获取子字符串。
   return(ss);               // 返回 "Spain"。
}

substring method

Returns the substring located at the specified position in the String object.

strVariable.substring(start, end)

"String Literal".substring(start, end)

Parameters

start

Indicate the starting position of the substring, the index starts from 0.

end

Indicates the end position of the substring. The index starts from 0.

Description

The substring method will return a string containing the substring from start to the end (excluding end).

The substring method uses the smaller of start and end as the starting point of the substring. For example, strvar.substring(0, 3) and strvar.substring(3, 0) will return the same substring.

If start or end is NaN or a negative number, replace it with 0.

The length of the substring is equal to the absolute value of the difference between start and end. For example, the length of the substring returned in strvar.substring(0, 3) and strvar.substring(3, 0) is 3.

Example

The following example demonstrates the use of the substring method.

function SubstringDemo(){
   var ss;                         // 声明变量。
   var s = "The rain in Spain falls mainly in the plain..";
   ss = s.substring(12, 17);       // 取子字符串。
   return(ss);                     // 返回子字符串。
}

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