Question

We can read properties like length and toUpperCase from string values. But if you try to add a new property, it doesn’t stick.

var myString = "Fido";
myString.myProperty = "value";
console.log(myString.myProperty);
// → undefined

Values of type string, number, and Boolean are not objects, and though the language doesn’t complain if you try to set new properties on them, it doesn’t actually store those properties. The values are immutable and cannot be changed.

But these types do have some built-in properties. Every string value has a number of methods. The most useful ones are probably slice and indexOf , which resemble the array methods of the same name.

console.log("coconuts".slice(4, 7));
// → nut
console.log("coconut".indexOf("u"));
// → 5

One difference is that a string’s indexOf can take a string containing more than one character, whereas the corresponding array method looks only for a single element.

console.log("one two three".indexOf("ee"));
// → 11

The trim method removes whitespace (spaces, newlines, tabs, and similar characters) from the start and end of a string.

console.log("  okay \n ".trim());
// → okay

We have already seen the string type’s length property. Accessing the individual characters in a string can be done with the charAt method but also by simply reading numeric properties, like you’d do for an array.

var string = "abc";
console.log(string.length);
// → 3
console.log(string.charAt(0));
// → a
console.log(string[1]);
// → b

This is a book about getting computers to do what you want them to do. Computers are about as common as screwdrivers today, but they contain a lot more hidden complexity and thus are harder to operate and understand. To many, they remain alien, slightly threatening things.