JavaScript has several built-in objects that are standardized by ECMAScript and implemented by browser vendors. These objects provide APIs for handling and manipulating data. There are ten main built-in objects in JavaScript, including: String, Boolean, Number, Array, Date, Math, Error, Function, Object, and Global. The wrapper types—String, Number, and Boolean—are used to encapsulate primitive data types and provide methods and properties for working with them.
The reason for using these wrapper types is to allow primitive values to have methods and properties, just like objects. Whenever you call a method on a primitive value or access its property, the JavaScript engine automatically creates a corresponding wrapper object. Once the operation is complete, the wrapper object is discarded. This means that strings, numbers, and booleans are immutable, and any modification must result in a new object being created.
The String object is used for processing text. You can create a string variable as a primitive type like this:
var stuName = 'Smith'; // direct reference var gender = 'male'; // direct reference var priceString = String(150.5); // type conversion
Or you can create a reference type string object using the new keyword:
var carType = new String('bmw528LI');
Some common String methods include:
str.length: returns the number of characters in the string.str.toLowerCase(): returns the string in lowercase.str.toUpperCase(): returns the string in uppercase.
For example:
var str = "Hello,World"; str = str.toLowerCase(); // "hello,world" var str1 = str.toUpperCase(); // "HELLO,WORLD" document.write(str + str1); // Output: hello,world HELLO,WORLD
Note that when you use string methods, you must assign the result to a new variable. Strings are immutable, so modifying them requires creating a new string. Also, when accessing characters, you can use charAt(index) to get the character at a specific position.
For example:
var pid = "371471194710040056"; var char = pid.charAt(pid.length - 2); console.log(char % 2 == 0 ? "Female" : "Male");
You can also encode and decode strings using charCodeAt() and fromCharCode(). For instance:
var input = prompt("Please enter the text to convert");
var result = [];
for (var i = 0; i < input.length; i++) {
result.push(input.charCodeAt(i));
}
document.write("The character you typed: " + input + "---" + " converted character: " + result.join(""));
When converting to five-digit codes, you can pad with zeros if the number is less than five digits. Decoding involves splitting the string into chunks of five digits and converting each back to a character.
Splitting strings is another common task, especially during interviews. Always use the new string after splitting, as the original cannot be modified directly. When optimizing string concatenation, it's more efficient to use arrays and then join them instead of repeatedly using the += operator.
String operations often involve searching for keywords, replacing them, and extracting substrings. The indexOf() and lastIndexOf() methods help locate occurrences of a substring, while slice() and substring() extract parts of a string. Regular expressions are also commonly used for pattern matching and replacement.
In summary, understanding JavaScript’s built-in objects and their methods is essential for effective string manipulation and overall programming. Proper use of these tools ensures clean, efficient, and readable code.
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