JavaScript second time Basic Learning notes (ii)

One, operator

　　1, unary operator:

　　　　Self-added self-reduction (2 types of front and rear): + + 、--

Difference: The first self-added or self-reduction, after the calculation, the second is the first to calculate, after the increase or decrease (in which it will have negative effects to reflect the difference);

var i=1; I+ +;  // ++i // no negative effects in case: 2/2 var a = (++i) +i;   var b = (i++) +I;console.log (a);   // 6Console.log (b);  // 7

It is suitable for any type, not a numeric type, to be converted to a numeric type number () ; (the literal of the underlying type cannot be used because it is immutable)

　　　　Add and Subtract operators: +,-

When its operand is not a number type, the operand is converted to number () type;

2, Bitwise operators:

Positive number: the original code representation;

Negative number: Complement expression (inverse code + 1);

Bitwise NON (~): negation code;

Bitwise AND (&): Both 1 is 1, the other is 0;

Bitwise OR (|): 1 is 1, both 0 is 0;

Bitwise XOR (^): At the same time 1, the difference is 0;

Shift Left (<<): vacancy 0;

Shift Right (>> sign bit): Empty fill sign bit;

Shift Right (>>> without sign bit): empty 0;

3. Boolean operator:

Logical non (!): Returns an inverse boolean value ;

Logic and (&&): Returns a Boolean value when both are Boolean values, not necessarily Boolean when there is not a Boolean value;

Logic or (| | ): Returns a Boolean value when both are Boolean values, not necessarily Boolean when there is not a Boolean value;

(Note: Logic and logic or both are short-circuiting operators )

4, Subtraction:

5, relational operators (>, >=, <, <=): are numeric, numeric comparisons, are string comparisons, and other conversions to a numerical comparison;

6, the equality operator (= =, = = =): Equal and congruent, congruent does not carry out type conversion;

7, three-wood operator (?:):;

......

Second, the statement:

1. If statement: Boolean () is converted to Boolean when the judging condition is non-boolean value;

2. Do-while: At least one cycle body is executed;

3. While:

4. For statement:

5. In statement: Used to enumerate object properties;

6. lable statement:

7. Break and Continue statements:

8. With statement: You can modify the scope to set the scope of the code to an object; with (...) { ... }

9. Switch statement:

3. Variables, scopes, and memory:

1. Value types and reference types: variables of value types hold specific values, whereas reference types are those that hold them;

2, the parameter of the function can pass only the value, so when the reference type is passed, its reference is passed;

3, the scope is defined when the non-call time;

function A () {  var t="aa";　　Function B () {Console.log (t); }  return  b; var t="ww"; var b=A (); B ();   // AA is not WW

4, extend the scope chain: Try-catch catch block and with;

5, JS no block-level scope;

　　　　

　　　　

JavaScript second time Basic Learning notes (ii)