JavaScript notes and summaries (2-3) JavaScript operators, control structures, and object operations

" Join operator +"

<script>Console.log (1+2+ ' a ' +3+4);</script> 

Output:

3a34

The logical operator returns the first value that can determine the result of an expression

Example ①

<script>varfalse; var b = Ten; var true ; var d = A | | B | | C;console.log (d); Console.log (typeof(d)); </script>

Output:

10

Number

Example ②

<script>var a = True; var B = False; var C = a && b;console.log (c); Console.log (typeof(c)); < ;/script>   

Output:

False

Boolean

Example ③ (&& priority above | | ）

<script>vartrue; var b = Ten; var false ; var d = A | | b && C;console.log (d); Console.log (typeof(d)); </script>

Output:

True

Boolean

Often used in some frameworks | | To do browser compatibility, form: WINDOW.A = WINDOW.A | | window.b

" iterating over an array "

<script>var arr = [' Hello ', ' world ',];  for (var i=0; i<arr.length; i++) {    console.log (arr[i]);} </script>

Output:

Hello

World

2015

" Traverse Object "

<script>var obj = {A: ' Hello ', B: ' World ', c:2015};  for (var in obj) {    Console.log (key+ ":" +Obj[key]);} </script>

Output:

A:hello

B:world

c:2015

" Object Actions "

When calling properties with native types such as numbers, strings, JS will instantly wrap these native types into objects

Example ①

<script>var str = "HelloWorld"; Console.log (str.length); </script>

Output 10

Example ②

<script>var str = "HelloWorld"; Console.log (str.substr (2,3)); </script>

Output: Llo

Example ③

<script>var arr = [' Arsenal ', ' Chelsea ', ' Manchester City ', ' Liverpool '];console.log (arr.join (')')var str = "Php,java,python"; Console.log (Str.split (', ')); </script>

Output:

Arsenal, Chelsea, Manchester City, Liverpool

["PHP", "Java", "Python"]

JavaScript notes and summaries (2-3) JavaScript operators, control structures, and object operations