executing for loop in javascript unsuccessful

Your problem is your conditional statement in the for loop:

i < obj[0].srcLanguageSentence.text;

You say that this loop should run for as long as i is less than obj[0].srcLanguageSentence.text, which looks wrong.

I guess you either want to run the for loop for every object in obj (as you take obj[i] in your code)? If so, write it like:

for (var i=0; i < obj.length; i++)

or, if it is for the length of the text:

for (var i=0; i < obj[0].srcLanguageSentence.text.length; i++)

With the incomplete snippet, there is hardly any detailed suggestion, though it looks like the issue is with your conditional statement. The general approach you may want to try, not only for this particular case, but for others as well, is adding more console.log to identify the issue, assuming u do not want to use the chrome debugger. For example,

var strArry = [];  

console.log(obj[0].srcLanguageSentence.text);
for(var i=0; i<obj[0].srcLanguageSentence.text; i++)
{
   console.log("enter:"+i);
    // create variables representing substrings of the Source language Sentence
    var s1 = text.substring((obj[i].srcLanguageSentence.roles[i].beginOffset - obj[i].srcLanguageSentence.roles[i].beginOffset),(obj[i].srcLanguageSentence.roles[i].beginOffset - 1));
  console.log('s1:'+s1);
    var s2 = text.substring(obj[i].srcLanguageSentence.roles[i].beginOffset,obj[i].srcLanguageSentence.roles[i].endOffset);
    var s3 = text.substring(obj[i].srcLanguageSentence.roles[i].endOffset,obj[i].srcLanguageSentence.text.length);

    strArry.push(s1)
    strArry.push(s2)

    if(i == obj[0].srcLanguageSentence.roles.length)
    {
        strArry.push(s3);
    }

    text =  s3;

 console.log("s1: " + s1);
 console.log("s2: " + s2);
 console.log("s3: " + s3);
 console.log(s1+s2+s3);
}

hope it helps.

Your loop is getting unsuccessful just because of your statement

for(var i=0; i<obj[0].srcLanguageSentence.text; i++)

Here in the for loop you need to put a condition in the numeric form and not in the string or text form.. Hence replace the condition in the looping statement and definitely you will get success in your loop.