For loop inside a string to concatenate the characters in a variable (without RegExp)- Javascript - Stack Overflow

I am trying to loop through a string variable and save every char inside an other variable. My code looks like this:

    var str = "hello world";
    var res = "";

    for (var i = str.indexOf("hello"); i <= str.lastIndexOf("hello"); i++) {
        res = res.concat(str.charAt(i));    
    }

    console.log("The result is: " + res);

It looks really logical for me, but it prints only the 1st letter. I expected it to say hello. What's the problem? Can't be done without a Regexp?

I am trying to loop through a string variable and save every char inside an other variable. My code looks like this:

    var str = "hello world";
    var res = "";

    for (var i = str.indexOf("hello"); i <= str.lastIndexOf("hello"); i++) {
        res = res.concat(str.charAt(i));    
    }

    console.log("The result is: " + res);

It looks really logical for me, but it prints only the 1st letter. I expected it to say hello. What's the problem? Can't be done without a Regexp?

• javascript
• for-loop
• concatenation
• indexof
• lastindexof

Share Improve this question Follow asked Aug 29, 2017 at 20:24 Manos ZManos Z 2511 silver badge55 bronze badges 2

• 3 str.lastIndexOf("hello") does not do what you think it does. It does not tell you where o is.... – epascarello Commented Aug 29, 2017 at 20:27
• this loop is only executed once – OneMoreQuestion Commented Aug 29, 2017 at 20:44

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3 Answers 3

Sorted by: Reset to default 1

You need the length and the start postion for checking the index.

var str = "bla bla hello world",
    res = "",
    i,
    l = "hello".length,
    p = str.indexOf("hello");

for (i = p; i < p + l; i++) {
    res += str[i];
}

console.log("The result is: " + res);

Replace str.lastIndexOf("hello") with pattern.length:

var str = "hello world";
var pattern = "hello";

var res = "";

var index = str.indexOf(pattern);

for (var i = index; i <= index + pattern.length; i++) {
  res = res.concat(str.charAt(i));
}

console.log("The result is: " + res);

From documentation:

The lastIndexOf() method returns the index within the calling String object of the last occurrence of the specified value, searching backwards from fromIndex. Returns -1 if the value is not found.

It's not the index of the last character.

For loop inside a string to concatenate the characters in a variable (without RegExp)

var theString = "This is my string";
var theArray = [];
var theResultString = "";

doIt(theString);
doitagain(theString)
function doIt(iningString)
{
  //concatenate into an array object
  for(var i = 0; i < iningString.length; i++)
    {
      theArray.push(iningString.substring(i, i+1))
    }
  console.log(theArray);
}

function doitagain(iningString)
{
  //concatenating into a string object
  for(var i = 0; i < iningString.length; i++)
  {
    theResultString += iningString.substring(i, i+1);
  }
  console.log(theResultString);
}