javascript substring

the most darndest thing! the following code prints out 'llo' instead of the expected 'wo'. i get such surprising results for a few other numbers. what am i missing here?

alert('helloworld'.substring(5, 2));

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Check the substring syntax:

substring(from, to)

from Required. The index where to start the extraction. First character is at index 0

to Optional. The index where to stop the extraction. If omitted, it extracts the rest of the string

I'll grant you it's a bit odd. Didn't know that myself.

What you want to do is

alert('helloworld'.substring(5, 7));

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alert('helloworld'.substring(5, 2));

The code above is wrong because the first value is the start point to the end point.E.g move from char 5 which is o and go to char 2 which is the l so will get llo So you have told it to go backwards.

What yuou want is

alert('helloworld'.substring(5, 7));

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最佳答案

You're confusing substring() and substr(): substring() expects two indices and not offset and length. In your case, the indices are 5 and 2, ie characters 2..4 will be returned as the higher index is excluded.

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See syntax below:

str.substring(indexA, [indexB])

If indexA > indexB, the substring() function acts as if arguments were reversed.

Consider documentation here: https://developer.mozilla.org/en-US/docs/JavaScript/Reference/Global_Objects/String/substring

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You have three options in Javascript:

//slice
//syntax: string.slice(start [, stop])
"Good news, everyone!".slice(5,9); // extracts 'news'


//substring
//syntax: string.substring(start [, stop])
"Good news, everyone!".substring(5,9); // extracts 'news'


//substr
//syntax: string.substr(start [, length])
"Good news, everyone!".substr(5,4); // extracts 'news'

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This is what I have done...

var stringValue = 'Welcome to India';


// if you want take get 'India'
// stringValue.substring(startIndex, EndIndex)
stringValue.substring(11, 16); // O/p 'India'