Functions Intro

Transcript

1. Functions executes code chunks when called http://www.w3schools.com/js/js_functions.asp Thursday, October 1, 2009
2. surprise! you already have been using them since your first line of code document.write, alert, prompt, confirm, parseInt, etc. Thursday, October 1, 2009
3. defining a function function foo() { // some code } Thursday, October 1, 2009
4. defining a function function foo() { // some code } function keyword Thursday, October 1, 2009
5. defining a function function foo() { // some code } function keyword function name Thursday, October 1, 2009
6. defining a function function foo() { // some code } function keyword function name parenthesis Thursday, October 1, 2009
7. defining a function function foo() { // some code } function keyword function name parenthesis start of function Thursday, October 1, 2009
8. defining a function function foo() { // some code } function keyword function name parenthesis start of function end of function Thursday, October 1, 2009
9. braces always mean start and stop (if, else if, else, for, for...in, while, functions, objects Thursday, October 1, 2009
10. calling a function // define function foo // for later use function foo() { // some code } // call the function and // run the code inside it foo(); Thursday, October 1, 2009
11. functions are called using parenthesis and the function name ( ) Thursday, October 1, 2009
12. calling a function // define function foo // for later use function foo() { // some code } // does not execute function foo; // executes function foo(); Thursday, October 1, 2009
13. var number_1 = 5; var number_2 = 10; var sum = number_1 + number_2; function foo() { alert('This will never alert.'); } alert(sum); // only sum will be alerted // the string inside foo function does // not because foo was never called the code inside functions only executes when the function is called Thursday, October 1, 2009
14. functions can return values // define the function function name() { return 'John Nunemaker'; } // call the function var name = name(); // name variable is now 'John Nunemaker' Thursday, October 1, 2009
15. the instant a return statement is found, the function returns and stops execution Thursday, October 1, 2009
16. function demoReturn() { return; // this will never be called alert('hi'); } // will not alert ‘hi’ demoReturn(); return doesn’t have to return a value Thursday, October 1, 2009
17. functions can have a parameter // define the function function name(name) { return 'The name was: ' + name; } // call the function var message = name('Ron Burgandy'); // message variable is now 'The name was: Ron Burgandy' // call the function again with different name message = name('Veronica Corningstone'); // message variable is now 'The name was: Veronica Corningstone' Thursday, October 1, 2009
18. functions can have a parameter // define the function function name(name) { return 'The name was: ' + name; } // call the function var message = name('Ron Burgandy'); // message variable is now 'The name was: Ron Burgandy' // call the function again with different name message = name('Veronica Corningstone'); // message variable is now 'The name was: Veronica Corningstone' name is a parameter Thursday, October 1, 2009
19. functions can have a parameter // define the function function name(name) { return 'The name was: ' + name; } // call the function var message = name('Ron Burgandy'); // message variable is now 'The name was: Ron Burgandy' // call the function again with different name message = name('Veronica Corningstone'); // message variable is now 'The name was: Veronica Corningstone' name is a parameter ‘Ron Burgandy’ is an argument ‘Veronica Corningstone’ is an argument Thursday, October 1, 2009
20. functions can have multiple parameters // define the function function fullName(first_name, last_name) { return first_name + ' ' + last_name; } var wes = fullName('Wes', 'Mantooth'); // wes variable is now 'Wes Mantooth' var brian = fullName('Brian', 'Fantana'); // brian variable is now 'Brian Fantana' Thursday, October 1, 2009
21. philosophical tidbit parameter - name of value to be used in function argument - value passed in when function called Thursday, October 1, 2009
22. camelCaseFunctionNames Thursday, October 1, 2009
23. naming conventions // variables use underscores var full_name = 'John Nunemaker'; // functions use camel case with lower first function fullName() { return 'John Nunemaker'; } Thursday, October 1, 2009
24. function can be made up of any code function demoWithLoop(loops) { for (var i=0; i < loops; i++) { alert("Why'd you have to wait..."); } } // two alerts demoWithLoop(2); Thursday, October 1, 2009
25. functions, ifs, loops function demoWithLoop(loops) { if (loops > 10) { alert('DO NOT WANT!'); } else { for (var i=0; i < loops; i++) { alert("Why'd you have to wait..."); } } } // alert DO NOT WANT! demoWithLoop(11); // 4 alerts of Why'd you have to wait... demoWithLoop(4); Thursday, October 1, 2009
26. functions, ifs, loops, return function demoWithLoop(loops) { if (loops > 10) { alert('DO NOT WANT!'); return; } for (var i=0; i < loops; i++) { alert("Why'd you have to wait..."); } } // alert DO NOT WANT! demoWithLoop(11); // 4 alerts of Why'd you have to wait... demoWithLoop(4); Thursday, October 1, 2009
27. assignment06 http://teaching.johnnunemaker.com/capp-30550/sessions/functions/ Thursday, October 1, 2009