The document covers JavaScript concepts like scoping, for loops, eval, with, arrays, equality comparisons, semicolons, commas, strict mode, and numbers. It provides examples to demonstrate variable scoping, proper for loop syntax, uses of eval(), the with statement, array creation and properties, equality vs identity operators, optional semicolons, comma operators, what strict mode does, and rounding errors with floating point numbers.

1. SCOPING

2. var i = 0;
function demo() {
for (i = 0; i < 10; i++) {
// blah
}
}
demo();
//what is i?

3. function demo() {
i = 50;
}
demo();
// what is i

4. var i = 0;
function demo() {
for (var i = 0; i < 10; i++) {
// blah
}
}
demo();
//what is i?

5. function demo() {
var i = 50;
}
demo();
// what is i

6. FOR LOOPS

7. for ([initialisation]; [condition]; [final-expression])
statement
Scenario 1: for (var i=0; i<10; i++) {}
Scenario 2: for (; i<10; i++) {}
Scenario 3: for (var i=10;; i++) {}
Scenario 4: for (var i=10; i<10;) {}
Scenario 5: for (; i<10;) {}
Scenario 6: for (;;) {}

8. EVAL

9. function setspan(num, text) {
eval("myspan"+num+".innerText" = "'"+text+"'");
}
eval("var a = 'awesome';");
print(a);
function doSomething(someValue) {
// …
}
setTimeout(“doSomething(‘times up’);”, 3000);
var sum = new Function(‘op1’, ‘op2’, ‘return op1 + op 2;’);
var result = sum(10, 20);

10. WITH

11. oo.ee.oo.ah_ah.bing = true;
oo.ee.oo.ah_ah.bang = true;
with (oo.ee.oo.ah_ah) {
bing = true;
bang = false;
}

12. oo.ee.oo.ah_ah.bing = true;
oo.ee.oo.ah_ah.bang = true;
var x = oo.ee.oo.ah_ah;
x.bing = true;
x.bang = false;

13. ARRAY

14. var a = new Array(5);
// length of array?
var b = new Array(5, 6);
// length of array?

15. var a = [];
// length of array?
var b = [5, 6];
// length of array?
ES5+
var buffer = new ArrayBuffer(16);
var int32View = new Int32Array(buffer);

16. EQUALITY

17. var x = “123”;
var y = 123;
x == y;

18. ‘’ == ‘0’
0 == ‘’
false == ‘false’
false == ‘0’
false == undefined
false == null
null == undefined
‘ trn’ == 0

19. ‘’ === ‘0’
0 === ‘’
false === ‘false’
false === ‘0’
false === undefined
false === null
null === undefined
‘ trn’ === 0

20. SEMICOLON

21. function x() {
return
5
}
x();

22. COMMA

23. var a = 1,2;
var b = 1,2,3;
var c = 99+1,99;

24. var j=0;
for (var i=0;i<10;i++, j++) {}
var r = [], n = 0, a = 0, b = 1, next;
function nextFibonacci() {
next = a + b;
return b = (a = b, next);
}
while(n++ < 10) {
r.push(nextFibonacci());
}

25. STRICT MODE

26. • What does it do?
• ECMAScript 3 deprecated methods raise exceptions
• Unassigned variables throw exceptions
• Delete throws exceptions
• Duplicate properties throw exceptions
• Hijacking eval throws exceptions
• Eval code is sandboxed
• With is gone
• MORE!!!
• Full info: http://dmitrysoshnikov.com/ecmascript/es5-chapter-2-strict-
mode/

27. “use strict”;
oo.ee.oo.ah_ah.bing = true;
oo.ee.oo.ah_ah.bang = true;
with (oo.ee.oo.ah_ah) { // error
bing = true;
bang = false;
}
var foo;
delete foo;

28. NUMBER

29. 0.1 + 0.2 === 0.3
(((a + b) + c) + d) === ((a + b) + (c + d))