Functions Review
Storing function evaluations
Functions within functions
Intro to Scope
1 var add = function(a, b) {
2
3 return a + b;
4
5 };
6
7 add(1, 2);
declaration / definition
invocation / call time
< Note 'function' keyword
< Note invocation
operator ()
1 var add = function (a, b) {
2
3 return a + b;
4
5 };
6
7 add(1, 2);
parameters
body
parameters
DRY: Do not repeat your code!
Expression: More expressive code!
User Input: We can create actions
without knowing the user input.
The value of a function is what is placed after its return statement.
1 var add = function(a, b){
2 return a + b;
3 };
4
5 add(4, 5);
^ When this line is run it would return 9, but we are not saving or displaying that return anywhere
How do we save function evaluations?
We can assign that value to a variable.
1 var add = function(a, b){
2 return a + b;
3 };
4
5 var sumOf4and5 = add(4, 5);
6
7 console.log(sumOf4and5); // => 9
^ Now our console would show 9
1 var add = function(a, b){
2 return a + b;
3 };
4 var sumOf4and5 = add(4, 5);
5 console.log(sumOf4and5); // => 9
6
7 var square = function(a){
8 return a * a;
9 };
10
11 var simpleSqVal = square(9);
12
13
14 console.log(simpleSqVal); // => 81
We can use the variable interchangeably with the value it stores
1 var add = function(a, b){
2 return a + b;
3 };
4 var sumOf4and5 = add(4, 5);
5 console.log(sumOf4and5); // => 9
6
7
8
9
10
11
12
13
14
1 var add = function(a, b){
2 return a + b;
3 };
4 var sumOf4and5 = add(4, 5);
5 console.log(sumOf4and5); // => 9
6
7 var square = function(a){
8 return a * a;
9 };
10 var ourSqVal = square(sumOf4and5);
11 var simpleSqVal = square(9);
12
13 console.log(ourSqVal); // => 81
14 console.log(simpleSqVal); // => 81
More complex functionality...
1 var addAndSquare = function(a, b){
2 var sum = a + b;
3 var square = sum * sum;
4 return square;
5 };
6
7 // This technique is called `imperative`
8 // programming. We are building out each
9 // step bit by bit.
Variables in the global scope can be accessed anywhere, and by anything in your function.
Variables in the local scope can only be accessed in that scope, or in 'child' scopes relative to that function.
var red = 'red';
var yellow = 'yellow';
var blue =
'blue';
console.log(red); // => 'red'
console.log(red); // => 'red'
A variable
can be called
from anywhere
within the scope
it is defined
console.log(red); // => 'red'
console.log(blue);
console.log(blue);
console.log(blue);
console.log(blue); // => undefined
console.log(blue); // => undefined
console.log(blue); // => 'blue'
1 var red = 'red';
2
3
4
5
6
7
8
9
10
1 var red = 'red';
2
3 var yellowScope = function() {
4 var yellow = 'yellow';
5
6
7
8
9
10 };
1 var red = 'red';
2
3 var yellowScope = function() {
4 var yellow = 'yellow';
5
6 var blueScope = function(){
7 var blue = 'blue';
8
9 };
10 };
1 var red = 'red';
2 console.log(red) // => 'red'
3 var yellowScope = function() {
4 var yellow = 'yellow';
5 console.log(red) // => 'red'
6 var blueScope = function(){
7 var blue = 'blue';
8 console.log(red) // => 'red'
9 };
10 };
1 var red = 'red';
2 console.log(blue) // => undefined
3 var yellowScope = function() {
4 var yellow = 'yellow';
5 console.log(blue) // => undefined
6 var blueScope = function(){
7 var blue = 'blue';
8 console.log(blue) // => 'blue'
9 };
10 };
Scope is the parent scope to the
`addAndSquare` function
Scope is child scope to the global object.
1 var globalScope = true;
2
3 var addAndSquare = function(a, b) {
4 var sum = add(a, b);
5 var squareSum = square(sum);
6 return squareSum;
7 };
Let's dive deeper into addAndSquare
var addAndSquare = function(a, b){
var sum = add(a, b)
var square = square(sum)
return square;
};
var eightyOne = addAndSquare(4, 5)
// inside of the local scope addAndSquare
// passing the arguments into `add` child scope
var sum = add(4, 5)
// inside local scope of `add` function
return 4 + 5
// inside of the local scope addAndSquare
var sum = add(4, 5)
// passing our sum into the square function
var square = square(sum)
return square;
// inside local scope of `square` function
return sum * sum
// back inside local scope of addAndSquare function
var sum = add(4, 5)
var square = square(sum)
// returning the square variable
return square;
// back in the global scope of the program
var addAndSquare = function(a, b){
var sum = add(a, b)
var square = square(sum)
return square;
};
// saving the returned results to the variable eightyOne
var eightyOne = addAndSquare(4, 5)
var addAndSquare = function(a, b){
var sum = add(a, b) // currently here
var square = square(sum)
return square;
};
var add = function(a, b){
return a + b // currently here
};
var addAndSquare = function(a, b){
var sum = add(a, b)
// currently here
var square = square(sum)
return square;
};
var square = function(num) {
return num * num // currently here
}
var addAndSquare = function(a, b){
var sum = add(a, b)
var square = square(sum)
// currently here
return square;
};
var eightyOne = addAndSquare(4, 5)
// currently here
var globalScope = true
var addAndSquare = function(a, b){
var sum = add(a, b)
var square = square(sum)
return square;
};
var eightyOne = addAndSquare(4, 5)