CODEWITHSUNDEEP
javascriptstringcharactersubstringline-breaks
ThomasReggi
ThomasReggi

Reputation: 59365

Get the line number of a string from body of text

Let's say I have a file with two lines and I get the indexOf a substring in the file. It returns with 18 the character that the substring is found at. How can I find the line with this information?

var file = [
  'var foo = "hello"',
  'console.log(foo)',
].join('\n')

var char = file.indexOf('console') // => 18
var line = lineOfChar(file, char) // => 2

Upvotes: 8

Views: 12753

Answers (3)

Wout De Rooms
Wout De Rooms

Reputation: 657

A possible way to achieve this, is to find the the string like you did with:

var index = file.indexOf('console'); // => 18

Then use this index to make a substring containing everything before that index:

var tempString = str.substring(0, index);

And lastly we count the occurrences of \n:

var lineNumber = tempString.split('\n').length;
// You should do - 1 if you want your 'first' line to be 0

Upvotes: 20

sheilak
sheilak

Reputation: 5873

function lineOf(text, substring){
  var line = 0, matchedChars = 0;

  for (var i = 0; i < text.length; i++) {
    text[i] === substring[matchedChars] ? matchedChars++ : matchedChars = 0;

    if (matchedChars === substring.length){
        return line;                  
    }
    if (text[i] === '\n'){
        line++;
    }
  }

  return  -1;
}

Avoids iterating over the string twice, once to find the substring and again to find the newlines.

Upvotes: 2

ThomasReggi
ThomasReggi

Reputation: 59365

var assert = require('assert')

var file = [
  'var alpha = "hello"',
  'var beta = "hello"',
  'var gamma = "hello"',
  'var delta = "hello"',
  'var episilon = "hello"'
].join('\n')

function getLine (body, charOrString) {
  if (!body) return false
  if (!charOrString) return false
  var char = (typeof charOrString === 'string') ? body.indexOf(charOrString) : charOrString
  var subBody = body.substring(0, char)
  if (subBody === '') return false
  var match = subBody.match(/\n/gi)
  if (match) return match.length + 1
  return 1
}

assert.equal(getLine(file, 'missing'), false)
assert.equal(getLine(file, 'alpha'), 1)
assert.equal(getLine(file, 'beta'), 2)
assert.equal(getLine(file, 'gamma'), 3)
assert.equal(getLine(file, 'delta'), 4)
assert.equal(getLine(file, 'episilon'), 5)

Upvotes: 2

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