JavaScript Notes _ Basic syntax

Like other programming languages, JavaScript also has variables, statements, functions, arrays and other common language elements.

1. Variables:

The variable is defined by the keyword var in javascript.

The variable type in JavaScript is a weak type (weak types are both not specified for specific data types)

Cases:

1. var x = 3;
2. x = "Hello";

Note: A special constant value in javascript: Undefined, when a variable is used without initialization, the value of the variable is undinfed (undefined).

2. Statement (same format as Java statement)

1) Judgment structure (if statement)

Cases:

1. if (x==4)//can perform comparison operations
2. if (x=0)//Can be assigned to the operation, and can also be sentenced, no error.

2) Select structure (switch statement)

Same as Java

3) Loop structure (while statement, do: While statement, for statement)

Example: (Print 99 multiplication table)

2. var x = "99 multiplication table";
4. alert (x);
8. document.write ("<table>");
10. for (var i=1; i<=9; i++)
12. {
14. document.write ("<tr>");
16. For (var j=1; j<=i; J + +)
18. {
20. document.write ("<th>");
22. document.write (j + "*" + i + "=" + i*j);
24. document.write ("</th>")
26. }
28. document.write ("</tr>");
30. }
32. document.write ("</table>");

Note: The difference is that there is no specific data type restrictions, use should be noted.

3. Functions (General format)

1) General format:

For example:

1. Function Show ()
2. {
3. Alert ("show");
4. alert (arguments.length);
5. }

Note: JavaScript functions, with no overloaded form of parameters. The parameters are uniformly placed inside the function's inner array arguments.

2) dynamic function definition (functions):

For example:

[JavaScript]View Plaincopy

1. var show = new Function ("x","y","return x+y;");
2. alert (show);

3) anonymous functions (typically used to define how events are handled):

For example:

[JavaScript]View Plaincopy

1. var show = function ()
2. {
3. Alert ("function run");
4. }
5. Show ();

4) Arguments array

JavaScript syntax, function, you can not explicitly declare the number and type of functions (not recommended), there is a default arguments array, can be dynamic acquisition of real parameters.

For example:

2. function Myadd ()
4. {
6. var sum = 0;
8. For (var x=0; x<arguments.length; x + +)
10. {
12. document.write ("Argu" + x + ":" + arguments[x] + "<br/>");
14. Sum + = arguments[x];
16. }
18. return sum;
20. }
22. document.write ("total:" + myadd (1,2,3,4) + "<br/>");

4. Arrays

JS, the array is equivalent to the collection in Java, the length is variable, there is no out of bounds.

Cases:

1. var arr = [4,1,6,8]; //directly define arrays
2. var arr = new Array (); //define an empty array
3. for (var i=0; i<arr.length; i++)
4. {
5. Alert (Arr[i]);
6. }

5, the definition of the object

2. The definition here is a bit like a constructor.
4. function person (name,age)
6. {
8. this.name = name;
10. this.age = age;
12. }
14. var p = New Person ("Mingzi","1");
16. P.getname = function () //tool method
18. {
20. return p.name;  //or return p["name"];
22. }

6. With statement

1. 6) withstatement
2. With (Stu) //stu is an object
3. {
4. Alert (name+"..." +age);
5. }

7. For-in statement

1) for-in traverse the properties of the class

1. For (S-in Stu) //s is the property name
2. {
3. Alert (Stu[s]);  //stu[s] is the property value corresponding to the S property in the Stu object.
4. }

2) for-in Traversal array

1. var array = [5,1,2,7];
2. For (the index in array)
3. {
4. document.write (Array[index] + "<br/>");
5. }

8. Adding methods to existing objects in JavaScript (using the prototype property)

For example: (for array classes, add Getmin () and Getmax () parties

2. Array.prototype.getMax = function ()
4. {
6. var max = This[0];
8. For (index in this )
10. {
12. if (This[index] > Max)
14. {
16. max = This[index];
18. }
20. }
22. return Max;
24. }
28. Array.prototype.getMin = function ()
30. {
32. var min = This[0];
34. For (index in this )
36. {
38. if (This[index] < min)
40. {
42. min = This[index];
44. }
46. }
48. return min;
50. }
54. var array = [1,4,3,3,5,6];
56. document.write (Array.getmax () + "<br/>");
58. document.write (Array.getmin () + "<br/>");
60. document.write ("<br/>");

JavaScript Notes _ Basic syntax