javascript substring

问题:

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));

回答1:

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.

回答2:

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'

回答3:

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));

回答4:

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));

回答5:

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

回答6:

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'