javascript.info (part 1)

You don’t need to define script type in the html <script> tags anymore.

‘+’ concatenates if at least one variable is a string whereas other mathematical operations convert variables to numbers.

PHP treats “0” as false, whereas Boolean(“0″) or (” “) in JS is true.

** is the exponentiation operator (2**3 = 8, 8**(1/3)=2)

++/– the prefix form changes assigned value, and postfix does not.

let counter = 1; let a = ++counter; // (*) alert(a); // 2

let counter = 1; let a = counter++; // (*) changed ++counter to counter++ alert(a); // 1

, operator evaluates serveral expressions and outputs the last result.

“a” > “A” == True because string comparison uses Unicode.

null == undefined // True (special rule), even though null becomes 0 and undefined Nan when converted to numbers.

alert( null > 0 ); // (1) false alert( null == 0 ); // (2) false alert( null >= 0 ); // (3) true

why: comparisons (>=, >) converts null to number (0), and equality (==) for null only equals undefined (and vice versa) but nothing else.

use ternary ‘?’ to return values, and ‘if’ to execute branches of code.

|| returns the last operand if no true operand is found.

AND returns the first falsy value or the last value if none were found.

The precedence of AND && operator is higher than OR ||.

A double NOT !! is sometimes used for converting a value to boolean type.

alert( !!"non-empty string" ); // true alert( !!null ); // false