variables, assignment and operators
Thursday, September 10, 2009
variablescontainers to store information
that can be used laterhttp://www.w3schools.com/JS/js_variables.asp
Thursday, September 10, 2009
Remember Algebra?5 = x + 3
Thursday, September 10, 2009
varvar a;var age = 5;var name = 'John Nunemaker';
Thursday, September 10, 2009
declaring variablesonly need var once, but multiple times won’t hurt you
// goodvar age = 15;age // 15age = 16;age // 16age = 17;age // 17
// no pointvar age = 15;age // 15var age = 16;age // 16var age = 17;age // 17
Thursday, September 10, 2009
undeclared variablesautomatically declare, but don’t do this
x = 10;foo = 'bar';
x // 10foo // "bar"
Thursday, September 10, 2009
variables can store anything
var age = 15;var name = 'John';var colors = ['red', 'green', 'blue'];var person = {name:'John', age:15};var cool = true;var foo = function() { return 'bar';}
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naming variablescase sensitive
var car = 'Ford';var cAr = 'Toyota';
car // "Ford"cAr // "Toyota"
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naming variablesmust begin with letter or underscore
var car; // good!var car9; // good!var _car; // good!var 9car; // bad! SyntaxError
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naming variablescan be short or descriptive
var x; // shortvar field; // descriptive
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naming variablesseparate words with underscores
var section_field_name; // good ideavar sectionfieldname; // bad idea
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naming variablesgeneral formatting rules for easier reading
var age = 15; // good ideavar age=15; // bad ideavar age = 15; // bad idea
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(pause for review and applause)
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good or bad?var section;
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good or bad?var section;
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good or bad?var 10thingsihateaboutyou;
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good or bad?var 10thingsihateaboutyou;
variables cannot start with numbers and should have underscores between words
Thursday, September 10, 2009
good or bad?var fieldname;
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good or bad?var fieldname;
Should be: var field_name;
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good or bad?var section_field_name;
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good or bad?var section_field_name;
Thursday, September 10, 2009
operatorsassignment and comparison
http://www.w3schools.com/JS/js_operators.asp
Thursday, September 10, 2009
arithmetic operators
operator meaning example result
+ addition 5 + 5 10
- subtraction 5 - 4 1
* multiplication 2 * 5 10
/ division 1 / 4 0.25
% modulus 5 % 4 1
++ increment x++ x + 1
-- decrement x-- x - 1
Thursday, September 10, 2009
assignment operators
operator example result same as
= var a = 5; 5
+= a += 5; 10 a = a + 5;
-= a -= 5; 0 a = a - 5;
*= a *= 2; 10 a = a * 2;
/= a /= 2; 2.5 a = a / 2;
%= a %= 4; 1 a = a % 4;
Thursday, September 10, 2009
comparison operators
operator meaning example result
equal to value 5 == 5 TRUE
equal to value and type
true === 1 FALSE
!= not equal 5 != 4 TRUE
> greater than 5 > 4 TRUE
< less than 5 < 4 FALSE
>=greater than or equal to
5 >= 5 TRUE
<=less than
or equal to5 <= 5 TRUE
==
===
http://www.w3schools.com/JS/js_comparisons.asp
Thursday, September 10, 2009
logical operators
operator meaning example result
&& and 5 == 5 && 4 != 6 TRUE
|| or 4 == 6 || 5 == 5 TRUE
! not !(5 == 4) TRUE
Thursday, September 10, 2009
putting it all together
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var a = 5;a += 3;a
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var a = 5;a += 3;a // 8
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var a = 2;var b = 5;a * b;
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var a = 2;var b = 5;a * b; // 10
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var a = 2;var b = 3;var c = a + b;var d = c * a;d
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var a = 2;var b = 3;var c = a + b;var d = c * a;d // 10
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var blue = 'blue';var red = 'red';var colors = [blue, red];colors
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var blue = 'blue';var red = 'red';var colors = [blue, red];colors // ["blue","red"]
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var a = 5;a = 6;a = 7;a -= 2;a
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var a = 5;a = 6;a = 7;a -= 2;a // 5
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var person = {name:'Peyton Manning'}person.name
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var person = {name:'Peyton Manning'}person.name // "Peyton Manning"
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var tv_shows = ['Wipeout', 'How I Met Your Mother', 'Big Bang Theory'];tv_shows[1] == 'How I Met Your Mother'
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var tv_shows = ['Wipeout', 'How I Met Your Mother', 'Big Bang Theory'];tv_shows[1] == 'How I Met Your Mother' // true
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var a = 5;var b = 4;var check = a == 5 && b == 3check
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var a = 5;var b = 4;var check = a == 5 && b == 3check // false
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var a = 5;var b = 4;var check = a == 3 || b > 3check
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var a = 5;var b = 4;var check = a == 3 || b > 3check // true
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var a = 5 - 1;a > 4
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var a = 5 - 1;a > 4 // false
Thursday, September 10, 2009
time to program
http://www.w3schools.com/JS/tryit.asp?filename=tryjs_intro
+ - * / % = == === != && || ! += -= /= *=
Thursday, September 10, 2009