JavaScript中的 ==、===、if()

转自 ：http://dorey.github.io/JavaScript-Equality-Table/

== (negated: !=)

When using two equals signs for JavaScript equality testing, some funky conversions take place.

true

false

1

0

-1

"true"

"false"

"1"

"0"

"-1"

""

null

undefined

Infinity

-Infinity

[]

{}

[[]]

[0]

[1]

NaN

Moral of the story:

Use three equals unless you fully understand the conversions that take place for two-equals.

===：

=== (negated: !==)

When using three equals signs for JavaScript equality testing, everything is as is. Nothing gets converted before being evaluated.

true

false

1

0

-1

"true"

"false"

"1"

"0"

"-1"

""

null

undefined

Infinity

-Infinity

[]

{}

[[]]

[0]

[1]

NaN

Moral of the story:

Use three equals unless you fully understand the conversions that take place for two-equals.

if():

A standard IF statement. If(value) {/*- green -*/} else { /*- white -*/ }

Note: This row does not match up with any of the rows in the other table.

true		if (true) { /* executes */ }
false		if (false) { /* does not execute */ }
1		if (1) { /* executes */ }
0		if (0) { /* does not execute */ }
-1		if (-1) { /* executes */ }
"true"		if ("true") { /* executes */ }
"false"		if ("false") { /* executes */ }
"1"		if ("1") { /* executes */ }
"0"		if ("0") { /* executes */ }
"-1"		if ("-1") { /* executes */ }
""		if ("") { /* does not execute */ }
null		if (null) { /* does not execute */ }
undefined		if (undefined) { /* does not execute */ }
Infinity		if (Infinity) { /* executes */ }
-Infinity		if (-Infinity) { /* executes */ }
[]		if ([]) { /* executes */ }
{}		if ({}) { /* executes */ }
[[]]		if ([[]]) { /* executes */ }
[0]		if ([0]) { /* executes */ }
[1]		if ([1]) { /* executes */ }
NaN		if (NaN) { /* does not execute */ }

Moral of the story:

Use three equals unless you fully understand the conversions that take place for two-equals.