Chap. 1 eloquent javascript Flashcards
(100 + 4) * 11
1,144
What character to use to get a space at “And”
“This is the first line And this is the second”
\n
write out:
“A newline character is written like “\n”.”
as code
“A newline character is written like "\n”.”
The following returns?
console.log(half of 100 is ${100 / 2} );
‘Half of 100 is 50’
${} is called
template literal
The following returns:
console.log(- (10 - 2))
-8
console. log(typeof 4.5)
console. log(typeof “x”)
// → number // → string
console.log(3 > 2)
// → true
console.log(3 < 2)
// → false
console.log(“Itchy” != “Scratchy”)
// → true
console.log(“Apple” == “Orange”)
// → false
console.log(NaN == NaN)
// → false
> =
greater than or equal too
<=
less than or equal too
!=
not equal too
= =
equal too
console.log(true && false)
// → false
console.log(true && true)
// → true
console.log(false || true)
// → true
console.log(false || false)
// → false
!true
False
!False
True
console.log(true ? 1 : 2);
// → 1
console.log(false ? 1 : 2);
// → 2
There are two special values, written ____ and ____, that are used to denote the absence of a meaningful value
Null
undefined
console.log(8 * null)
// → 0
console.log(“5” - 1)
// → 4
console.log(“5” + 1)
// → 51
console.log(“five” * 2)
// → NaN
console.log(false == 0)
// → true
console.log(true == 0);
// → false
When something that doesn’t map to a number in an obvious way (such as “five” or undefined) is converted to a number, you get the value
NaN
console.log(null == undefined);
// → true
console.log(null == 0);
// → false
console.log(“ “ == false);
// → true
console.log(“ “ === false);
// → false
console.log(null || “user”)
// → user
console.log(“Agnes” || “user”)
// → Agnes
console.log(NAN || “user”)
reference error
The rules for converting strings and numbers to Boolean values state that 0, NaN, and the empty string (“”) count as
false
console.log(0 || -1)
-1
console.log(0 && -1)
0
console.log(-1 && 0)
0
console.log(-1 || 0)
-1
console.log(1 - 2 + 1)
0
console.log(NaN == NaN)
flase
There is only one value in JavaScript that is not equal to itself, and that is ______
NaN
console.log(true !& true)
syntax error
var a = 3; var b = -2; console.log(!(a > 0 || b > 0));
// false
If expr1 can be converted to true, returns expr2; else, returns expr1.
&& operator
If expr1 can be converted to true, returns expr1; else, returns expr2.
|| operator
Examples of expressions that can be converted to false are:
null;
NaN;
0;
empty string ("" or '' or ``);
undefined.`console.log(true || false && false); why?
// returns true, because && is executed first
console.log((true || false) && false); why?
// returns false, because operator precedence cannot apply
n3 = !’’
// !f returns true
n4 = !’Cat’
// !t returns false
true || true
//true
o2 = false || true
// true
o3 = true || false
// true
o4 = false || (3 == 4)
// false
o5 = ‘Cat’ || ‘Dog’
//”Cat”
o6 = false || ‘Cat’
//”Cat”
o7 = ‘Cat’ || false
// “Cat”
o8 = ‘’ || false
// false
o9 = false || ‘’
// “”
o10 = false || varObject /
// varObject
bCondition1 && bCondition2
is always equal to:
!(!bCondition1 || !bCondition2)
bCondition1 || bCondition2
is always equal to:
!(!bCondition1 && !bCondition2)
!!bCondition
is always equal to:
bCondition
console. log(true && true);
console. log(true && false);
console. log(false && true);
console. log(false && false);
true
false
false
false
console. log(true || true);
console. log(true || false);
console. log(false || true);
console. log(false || false);
true
true
true
false
This operator is frequently used as an alternative to an if…else statement.
Conditional (ternary) operator
