This the slide stack for the two videos on Data types in my YouTube series on JavaScript. The videos are at https://www.youtube.com/watch?v=UAtJXkGggOU and https://www.youtube.com/watch?v=H2sjsGZyYaw

1. JavaScript
Data Types (part
1)
Charles Russell
Bennu Bird Media

2. JavaScript is a Typed
language
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Weakly typed does not mean type unaware
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There are 6 types in JavaScript
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Boolean
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Number
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String
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Null
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Undefined
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Object
– Complex Data type
– Array

3. typeof Operator
Type val Returns
Undefined 'undefined'
Null 'object'
Boolean 'boolean'
Number 'number'
String 'string'
Object (native and does not implement
[[Call]])
'object'
Object (native or host and does implement
[[Call]])
'function'
Object (host and does not implement [[Call]]) Implementation-defined except may not be
"undefined", "boolean", "number", or "string".
ECMA 262 Table 20
typeof val

4. But Null is not an object
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In chapter 8 of the standard Null is declared to be
a primitive type.
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typeof returns object on null because the standard
says to
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The only short justification I have seen is from Kiro
Risk
– The reasoning behind this is that null, in contrast with
undefined, was (and still is) often used where objects
appear. In other words, null is often used to signify an empty
reference to an object. When Brendan Eich created
JavaScript, he followed the same paradigm, and it made
sense (arguably) to return "object". In fact, the ECMAScript
specification defines null as the primitive value that

5. Null
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As just discussed this is the intentional absence of
any value .
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Has only one value null
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Any variable that is set to null is not undefined
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It just has no value

6. Undefined defined
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The Undefined type has exactly one value, called
undefined. Any variable that has not been
assigned a value has the value undefined. ECMA
262 5.1

7. Objects an introduction
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Everything that is not a primitive type a is an
object type (remember this it is important later)
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Properties are charcteristics
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Methods are actions
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In JavaScript unlike other languages, objects are
dynamic
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They can be changed modified and extended at
runtime
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They can have any value except undefined
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Represented as name value pairs in code

8. Boolean
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Can have one of two values
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true
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false
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Boolean()
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methods
– toString()
– valueOf()
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Falsey
– Values that when checked evaluate to false
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0 or -0
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EmptyString ""

9. Next Data Types (part 2)

10. Number
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Represented internally as a floating point
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This has some implications.
– Decimals values are approximations
– 0.1 + 0.2
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Expected Value 0.3
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Returned value 0.30000000000000004
– Problem not unique to JavaScript
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All languages that impliment floating point have the issue
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Technical reason at The reason in detail is at
http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html
for those with a technical or mathematical disposition.
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When dealing with money covert to cents do the math then convert
back

11. Number (cont)
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NaN
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NaN stands for Not a Number
– But it is if typeof reports it as a Number
– This is the result of bad calculation such as division by 0
– NaN is not equal to anything even NaN
– Any calculations with NaN results in NaN
●
IsNaN() will check to see if a value is NaN
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Number()
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toExponential()
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toFixed()
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toPrecision()

12. Number(yes a little more)
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parseInt(value, radix)
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Another way to convert a string to a number
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Radix
– Base 10 the number system we all use is not the only one
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Octal base 8
– 8 digits 0...7
– 10 = 8, 11=9, 12=10, ….
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Hexadecimal Base 16
– 15 digits 0..9 then A..F
– A = 10, B = 11, … F=15, 10=16, 11=17, ….
– Leading with 0 makes value ocal, 0x hexadecimal
– Older browsers the value defaulted to octal so use the radix
can be value 1..32 10 would be the radix that we Humans
like the best

13. The Math Object
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The Math Object is automatically created and is
globally available
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Methods include
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floor()
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round()
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sin()
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cos()
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tan()
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random()
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And many more

14. Strings
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0 or more characters represented as two hex
digits
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UTF-16, for older browsers UCS2
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There is no char data type as in other languages
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Here the equivilent is a string of length 1
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Empty string
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X=““ is a string of length 0 in other words typeof
returns string

15. Strings(cont)
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String literals
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Are surrounded by Double " or single quotes '
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Quotes can not be nested in quotes of the same type
– 'this will "work" fine'
– 'this will 'not work' at all'
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toString()
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Available on most wrapper type converts values to
their string equivalents
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Can't handle null or undefined

16. Strings (yea theres more)
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Escape characters
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allows you to use some special characters
– ' allows you to use ' inside of a single quoted string
– “ allows you to use double quotes in a double quoted string
– n newline
– t tab
– backslash (escaping the escape)

17. Some String Properties
and Methods
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String()
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length
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substr()
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toLowerCase()
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toUpperCase()
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split()
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splice()

18. Summary
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JavaScript primatives are Null, Undefined,
Boolean, Number, String and Object
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The typeof operator can tell you the object type of
a variable
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There are wrapper Objects for most primatives
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These wrapper object have useful methods
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Most things in JavaScript are objects

19. Next: A Demo and then Operators