How to Compare Strings in JavaScript

Introduction to JavaScript String Comparison

JavaScript offers a set of predefined methods that allow access to client-side web user data, enabling various operations to meet user requirements without necessitating backend technology. One such predefined method is the localeCompare() function, which compares two strings within the scripting language. If the function returns 0, it indicates that the two string values are equal. This will return -1 for the case of the first string ordered before the second, and 1 for the case of the second string ordered before the first one.

Syntax:

The localeCompare() method compares two sets of string values in JavaScript. It follows a fundamental format for implementation in client-side code.

The above codes illustrate the basic syntax involved in the string comparison function, which is used through localeCompare() in the HTML format of a web page with its script logic. Though the function can be used independently without further function definitions, the <script> tag is needed to initialize the method on the web page.

How Does String Comparison in JavaScript Function?

There are several inbuilt methods that are highly applied in client-side scripting in JavaScript programming within web development. JavaScript also supports both strict comparisons and those involving type conversion. The strict comparison, which is denoted by the operator ===, is used to find out whether two operands have the same data type as well as hold the same content, such as equal string values. In most instances, the == operator is used in comparison of value, and such an operator will behave like strict comparison except that before making the actual comparison, both operands are first coerced into the same kind of data. Other relational operators applied in JavaScript are <=, whereby two operands are evaluated before their first operand is coerced into its primitive type before proceeding with the evaluation of the expression.

Strings are normally sorted in standard lexicographical order according to their Unicode values. For two strings to be equal, their character sequences must be identical, their lengths must coincide, and they must contain the same characters at corresponding positions. Two numbers are also said to be strictly equal if they have the same value. In certain cases, NaN is an operand value for strings, and it must be known that positive and negative zeros are equal. When the operands do not have the same type in a comparison of string values, strict comparisons must be used. When the operands are of objects, JavaScript checks their references. It determines equality only when both operands refer to the same memory instance.

If the operands are found to be different, the relational operator requires the operands to have the same type. In the case of JavaScript, the language attempts to change the operands into a suitable type for comparison purposes. In comparing two operands that are instances or objects, JavaScript checks their internal references; when the operands point to different objects in memory, they are regarded as unequal. Identity operators return a true value only when the operands are strictly equal, allowing no type conversion. The non-identity operator (!==) returns a true value when the operands are different and also of different types. Standard equality operators, such as == and!= use the Abstract Equality Comparison Algorithm to determine the relationship of two operands.

In the case of different operand types, the algorithm automatically converts them into a common type before making a comparison.

Examples of JavaScript Compare Strings

Here are various examples demonstrating how to compare strings in JavaScript.

Example 1

Code

Output

After clicking the button:

Case-Insensitive String Comparison

For example, one can request a user to input names and later check if such names are in our database. In this case, the two strings need not be identical; that is, case differences are allowed. Such are cases of case-insensitive string comparisons.

In the string comparison method, case-insensitive means that case, such as whether uppercase letters or lowercase letters are used, are ignored. In JavaScript, toLowerCase() and toUpperCase() are used to compare two strings case-insensitive.

Example 2

Code

Output

In the above example, comparing str1 and str2 after the toUpperCase method is applied makes the expression JAVASCRIPT == JAVASCRIPT true, which means the two strings are the same when they are converted to upper case. The equality operator (==) checks whether the two strings are equal.

In the following example, the comparison of str1 and str3 after both have been subjected to the toUpperCase method results in the statement javascript == javascript also being true because both strings are identical when in lowercase.

In the last example, comparing str1 and str4 causes the expression JavaScript == Typescript to evaluate to be false because JavaScript and Typescript are two different strings.

Conclusion

In JavaScript, the string data type declared variable should be compared with the help of comparison operators, which return a boolean value. Such comparison can also include different conditional operators.