- 3.1 Declaring Functions
- 3.2 Higher-Order Functions
- 3.3 Function Literals
- 3.4 Arrow Functions
- 3.5 Functional Array Processing
- 3.6 Closures
- 3.7 Hard Objects
- 3.8 Strict Mode
- 3.9 Testing Argument Types
- 3.10 Supplying More or Fewer Arguments
- 3.11 Default Arguments
- 3.12 Rest Parameters and the Spread Operator
- 3.13 Simulating Named Arguments with Destructuring
- 3.14 Hoisting
- 3.15 Throwing Exceptions
- 3.16 Catching Exceptions
- 3.17 The finally Clause
- Exercises
This chapter is from the book
This chapter is from the book
This chapter is from the book
3.3 Function Literals
Let us continue the example of the preceding section. Suppose we want to multiply all array elements by 10. Of course, we can write a function
function multiplyBy10(x) { return x * 10 }
Now we can call:
result = [0, 1, 2, 4].map(multiplyBy10)
But it seems a waste to declare a new function just to use it once.
It is better to use a function literal. JavaScript has two syntactical variants. Here is the first one:
result = [0, 1, 2, 4].map(function (x) { return 10 * x })
The syntax is straightforward. You use the same function syntax as before, but now you omit the name. The function literal is a value that denotes the function with the specified action. That value is passed to the map method.
By itself, the function literal doesn’t have a name, just like the array literal [0, 1, 2, 4] doesn’t have a name. If you want to give the function a name, do what you always do when you want to give something a name—store it in a variable:
const average = function (x, y) { return (x + y) / 2 }
TIP
Think of anonymous function literals as the “normal” case. A named function is a shorthand for declaring a function literal and then giving it a name.