javascript

Chapter 3: Language Basics
Most of the time you’ll be parsing decimal numbers, so it’s good to always include
10 as the second argument.
The parseFloat() function works in a similar way to parseInt() , looking at each character starting in
position 0. It also continues to parse the string until it reaches either the end of the string or a character
that is invalid in a floating - point number. This means that a decimal point is valid the first time it
appears, but a second decimal point is invalid and the rest of the string is ignored, resulting in
“22.34.5” being converted to 22.34.
Another difference in parseFloat() is that initial zeros are always ignored. This function will recognize
any of the floating - point formats discussed earlier, as well as the decimal and octal integer formats.
Hexadecimal numbers always become 0. Because parseFloat() parses only decimal values, there is no
radix mode. A final note: if the string represents a whole number (no decimal point or only a zero after
the decimal point), parseFloat() returns an integer. Here are some examples:
var num1 = parseFloat(“1234blue”); //1234 - integer
var num2 = parseFloat(“0xA”); //0
var num3 = parseFloat(“22.5”); //22.5
var num4 = parseFloat(“22.34.5”); //22.34
var num5 = parseFloat(“0908.5”); //908.5
var num6 = parseFloat(“3.125e7”); //31250000
The String Type
The String data type represents a sequence of zero or more 16 - bit Unicode characters. Strings can be
delineated by either double quotes ( “ ) or single quotes ( ‘ ), so both of the following are legal:
var firstName = “Nicholas”;
var lastName = ‘Zakas’;
Unlike PHP, for which using double or single quotes changes how the string is interpreted, there is no
difference in the two syntaxes in ECMAScript. A string using double quotes is exactly the same as a
string using single quotes. Note, however, that a string beginning with a double quote must end with
a double quote, and a string beginning with a single quote must end with a single quote. For example,
the following will cause a syntax error:
var firstName = ‘Nicholas”;
//syntax error - quotes must match
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