JavaScript: Variables and Functions
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This document discusses JavaScript variables, functions, and objects. It covers JavaScript datatypes like numbers, strings, and objects. It describes variable scope and how variables are hoisted or moved to the top of their function. It also discusses how functions can be defined and used as variables. Global objects like the window object are described. Finally, it provides examples of defining basic functions and using objects with properties and methods.
JavaScript: Variables and Functions
- 1. JS Variables and Func1ons Jussi Pohjolainen Tampere University of Applied Sciences
- 2. Datatypes • Numbers • Boolean • String • Null, undefined • Object • Func1on
- 3. Variable scope • Global and local variables • JS does not have block statement scope! function test() { if(true) { var x = 5; } document.write(x); } • This works! X is defined in the scope of the func1on (or globally)
- 4. Hois1ng • Variables are moved on top of the func1on! function test() { var x; if(true) { x = 5; } document.write(x); }
- 5. Hois1ng function test() { document.write(x); // Prints undefined! if(true) { var x = 5; } }
- 6. Hois1ng function test() { var x; document.write(x); // Prints undefined! if(true) { x = 5; } }
- 7. So what happens here? var x = 10; function test() { document.write(x); if(true) { var x = 5; } }
- 8. So what happens here? var x = 10; function test() { var x; // Overrides the global one.. document.write(x); // undefined if(true) { x = 5; } }
- 9. Global Objects • Global variables are in fact proper1es of the global object! • In web pages the global object is window • So – var x = 5 ó window.x = 5;
- 10. Objects var Sales = "Toyota"; function CarTypes(name) { if (name == "Honda") return name; else return "Sorry, we don't sell " + name + "."; } var car = { myCar: "Saturn", getCar: CarTypes("Honda"), special: Sales }; document.write(car.myCar); // Saturn document.write(car.getCar); // Honda document.write(car.special); // Toyota
- 11. Basic Func1on function add(a, b) { return a+b; } alert(add(1,2));
- 12. Func1on as Variable var add = function(a, b) { return a+b; } alert(add(1,2));
- 13. Func1on as Variable var add=function theAdd(a, b) { return a+b; } alert(add(1,2)); // produces 3 alert(theAdd(1,2)); // also produces 3