Compare Two Strings

By Stephen Bucaro

In programming, the word "string" refers to an array of characters like a sentence or a paragraph. You can compare two strings using == (the equality operator) as shown below.

var a = "yesterday";
var b = "Yesterday";

if(a == b)
  alert("The strings are identical");
else
  alert("The strings are different");

When we compare strings this way, we are simply comparing their ASCII or Unicode data as if they were numeric values. This type of comparison is case sensitive. In the example above, a comparison would say that the two strings are different because of the case difference in the first letter. To return a positive result each character in the first string must be the same case as the corresponding character in the second string.

 Java Script provides a built-in string object that provides you with many methods for manipulating strings. Proper coding would declare string variables as shown below.

var a = new String("yesterday");
var b = new String("Yesterday");

But strictly speaking, you don't have to declare the variables to be String objects because when you put the left-value within paracentesis, Java Script automatically stores them in String objects.

But what if we didn't care about case? The string object contains two methods; toUppercase and toLowercase that lets you change the case of all the characters in a string. The code below uses the toUppercase method to change both strings to all uppercase characters before making a comparison.

var strOne = new String("yesterday");
var strTwo = new String("Yesterday");
if(strOne.toUpperCase() == strTwo.toUpperCase())
   alert("The strings are identical");
else
   alert("The strings are different");

In the example above, a comparison would say that the two stings are identical because the toUppercase changed the value of strOne to "YESTERDAY" and the value of strTwo to "YESTERDAY" before the comparison was made.

One common problem with string comparisons, especially when one of the strings was acquired from a form textbox, is blank characters on the beginning or end of a string. The Java Script object does not contain a built-in method to trim leading and trailing blanks from a string.

function trimString(aString) 
{
  while(aString.substring(0,1) == ' ')
  {
    aString = aString.substring(1, aString.length);
  }
  while(aString.substring(aString.length - 1, aString.length) == ' ')
  {
    aString = aString.substring(0,aString.length-1);
  }
  return aString;
}

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