Introduction to the usage of the methods slice()&substring()&substr() of the String object in js

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The methods slice(), substring(), and substr() (deprecated) of the String object can all return a specified portion of a string. slice(start, end) is more flexible than substring(start,stop) because it allows negative numbers as arguments. slice(start,end) differs from substr(start,length) in that it specifies the substring in terms of two character positions, whereas substr(start,length) specifies the substring in terms of character position and length.
Also note that String.slice() is similar to Array.slice().

String

Syntax for creating a String object

new String(s); String(s);

Parameters

The parameter s is the value to be stored in the String object or converted to a raw string.

Return value

When String() is used as a constructor together with operator new, it returns a newly created String object, which stores the string s or s String representation.

When String() is called without the new operator, it simply converts s to the original string and returns the converted value.

slice

Syntax

stringObject.slice(start,end)

Parameter Description

start The starting index of the segment to be extracted. If it is a negative number, this parameter specifies the position starting from the end of the string. That is, -1 refers to the last character of the string, -2 refers to the second to last character, and so on.
end The index immediately following the end of the segment to be extracted. If this parameter is not specified, the substring to be extracted includes the string from start to the end of the original string. If this parameter is negative, it specifies the position from the end of the string.

Return value

A new string. Includes all characters of the string stringObject from start (inclusive) to end (exclusive).

substring

Syntax

stringObject.substring(start,stop)

Parameter Description

start Required. A nonnegative integer that specifies the position in stringObject of the first character of the substring to be extracted.
stop Optional. A nonnegative integer that is one position in the stringObject that is one more than the last character of the substring to be extracted. If this parameter is omitted, the returned substring will go to the end of the string.

Return value

A new string value contains a substring of stringObject, and its content is everything from start to stop-1 (excluding stop) Characters whose length is stop minus start.

Explanation

The substring() method returns the substring including the characters at start, but does not include the characters at stop.

If the parameters start and stop are equal, then this method returns an empty string (that is, a string with a length of 0). If start is greater than stop, the method swaps the two arguments before extracting the substring.

Tips and Notes

Important: Unlike the slice() and substr() methods, substring() does not accept negative arguments.

substr (not recommended)

Syntax

stringObject.substr(start,length)

Parameter Description

start Required. The starting index of the substring to be extracted. Must be a numeric value. If negative, this parameter declares the position from the end of the string. That is, -1 refers to the last character in the string, -2 refers to the second to last character, and so on.

length Optional. The number of characters in the substring. Must be a numeric value. If this parameter is omitted, the string from the beginning to the end of stringObject is returned.

Return value

A new string containing length characters starting from the start of stringObject (including the character pointed to by start). If length is not specified, the returned string contains characters from start to the end of the stringObject.

Tips and Notes

Note: The parameters of substr() specify the starting position and length of the substring.

Important matters:

ECMAscript does not standardize this method and therefore discourages its use.

Related recommendations:

Analysis of slice() method of String object in javascript_javascript skills

js Instructions for using slice() method_Basic knowledge

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