Introduction

In languages like C, we are used to thinking about data types separately from the functions that operate upon them. We declare variables to hold data in memory, and call functions passing them variables as arguments to operate on their values.

In object-oriented languages like JavaScript, we are able to combine data and functionality into higher order types, which both contain data and allow us to work with that data. In other words, we can pass data around in a program, and all the functionality that works on that data travels with it.

Let's consider this idea by looking at strings in C vs. JavaScript. In C a string is a null terminated (\0) array of char elements, for example:

const char name1[31] = "My name is Arnold";
const char name2[31] = {'M','y',' ','n','a','m','e',' ','i','s',' ','A','r','n','o','l','d','\0'};

With C-style strings, we perform operations using standard library functions, for example string.h:

#include <string.h>

int main(void)
{
    char str[31];        // declare a string
    ...
    strlen(str);         // find the length of a string str
    strcpy(str2, str);   // copy a string
    strcmp(str2, str);   // compare two strings
    strcat(str, "...");  // concatenate a string with another string
}

JavaScript also allows us to work with strings, but because JavaScript is an object-oriented language, a JavaScript String is an Object with various properties and methods we can use for working with text.

One way to think about Objects like String is to imagine combining a C-string's data type with the functions that operate on that data. Instead of needing to specify which string we want to work with, all functions would operate a particular instance of a string. Another way to look at this would be to imagine that the data and the functions for working with that data are combined into one more powerful type. If we could do this in C, we would be able to write code that looked more like this:

String str = "Hello"; // declare a string

int len = str.len;    // get the length of str
str.cmp(str2);        // compare str and str2
str = str.cat("..."); // concatenate "..." onto str

In the made-up code above, the data (str) is attached to functionality that we can call via the .* notation. Using str.*, we no longer need to indicate to the functions which string to work with: all string functions work on the string data to which they are attached.

This is very much how String and other Object types work in JavaScript. By combining the string character data and functionality into one type (i.e., a String), we can easily create and work with text in our programs.

Also, because we work with strings at a higher level of abstraction (i.e., not as arrays of char), JavaScript deals with memory management for us, allowing our strings to grow or shrink at runtime.