Usage and difference between substr and substring in JS

Both substr and substring are JS string truncation functions. The two functions are similar in usage, but they are different in many places. Next I will summarize the usage and differences between substr and substring.

The syntax of the two is as follows:

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

Stringvar. substr (start [, length])
Parameters
Stringvar
Required. The String text or String object to extract the substring.
Start
Required. The starting position of the required substring. The index of the first character in the string is 0.
Length
Optional. The number of characters to be included in the returned substring.

Description
If the length is 0 or negative, an empty string is returned. If this parameter is not specified, the substring will continue to the end of stringvar.

Sample Code

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Function SubstrDemo (){ Var s, ss; // declare the variable. Var s = "The rain in Spain falls mainly in the plain ."; Ss = s. substr (12, 5); // obtain the substring. Return (ss); // return "Spain ". }

Substring Method
Returns the substring at the specified position in the String object.

StrVariable. substring (start, end)

"String Literal". substring (start, end)
Parameters
Start
Specifies the starting position of the substring. The index starts from 0.
End
Specifies the end position of the substring. The index starts from 0.

Description
The substring method returns a string that contains a substring from start to the end (excluding end.
The substring method uses a small value in start and end as the starting point of the substring. For example, strvar. substring (0, 3) and strvar. substring (3, 0) return the same substring.
If start or end is NaN or negative, 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.

Sample Code

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Function SubstringDemo (){ Var ss; // declare the variable. Var s = "The rain in Spain falls mainly in the plain .."; Ss = s. substring (12, 17); // obtain the substring. Return (ss); // returns a substring. }

Method for ending the last character of a string

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Var str = "aaaaaaaaaaaaaaaaaa | "; Var texts = str. substr (0, str. length-1 ); Alert (texts );

[Note]: the length of a string with spaces after the substr and substring functions are used is the length of each space. For example:

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Var a = "I am shi huan !"; A. substring (0, 5). length

The value is 5 instead of 4,

But alert (. substring (0, 5); the value is I am, so that alert ("I am" =. substring (0, 5 );

When is false,

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Alert ("I am" = a. substring (0, 4 ));

True.