Javascript interview question 1

1. What is the value of Y and Z?
<SCRIPT type = "text/JavaScript">
VaR x = 1;
Var y = 0;
VaR z = 0;
Function add (n) {n = n + 1 ;}
Y = add (X );
Function add (n) {n = N + 3 ;}
Z = add (X );
</SCRIPT>
All are undefined, because there is no return value.

2. Javascript is object-oriented. How does one reflect the inheritance relationship of JavaScript?
Use prototype.

3. How does JavaScript select a checkbox and set it to invalid?
Document. All. CB1 [0]. Disabled = true;

4. The input in form can be set to readonly and disable. What is the difference between them?
Readonly cannot be edited, but can be selected and copied; values can be passed to the background
Disabled cannot be edited, copied, or selected; value cannot be passed to the background

5. What are the imperative types of three pop-up message reminders (warning window, confirmation window, and Information Input window) in JS?
Alert
Confirm
Prompt

6. What types of input are in form?

7. What are the differences between the two types of JavaScript variables?

Global variable: valid on the current page

Local variable: valid in Method

8. list three main data types of JavaScript, two composite data types, and two special data types.

Main data types: String, Boolean, number

Composite data type: function, Object

9. How to capture exceptions in the program?

Window. Error

Try {} catch () {} finally {}

10. Write the returned results of the datedemo function. The system time is assumed to be today.

Function datedemo (){

VaR D, S = "today's date is :";

D = new date ();

S + = D. getmonth () + "/";

S + = D. getdate () + "/";

S + = D. getyear ();

Return S;

}

Result: The current date is 7/17/2010.

11. Write the program running result?

For (I = 0, j = 0; I <10, j <6; I ++, J ++ ){

K = I + J;

}

Result: 10(Careful traps)

12. What are the running results?

Function hi (){
VaR;
Alert ();
}

Result: Undefined

13. What are the running results?

Function hi (){
VaR A = NULL;
Alert ();
}

Result: null.

14. What is the browser's object model?

Window

Top-level object

Window. Alert (MSG)

Window. Prompt ()

Window. Confirm ()

If (window. Confirm ()){

...

}

Window. open ()

Window. Close ()

Document

Document. Write ()

History

When a user browses a webpage, the browser saves a list of URLs of the recently accessed webpage. This list is represented by the history object.

History. Back (): Back

History. Forward (): Forward

History. Go (n): positive number indicates forward, negative number indicates backward

Location

Indicates the URL Information of the currently opened window or framework.

Location. href: Redirection

Equivalent to location. Assign (URL)

Location. HOST: similar to www.163.com: 80

Navigator

Indicates the browser information and JS running environment

Navigator. cookieenabled: Indicates whether to enable cookie.

Screen

Display the display size and color of a webpage

Screen. width/screen. Height: Display resolution (total width, height)

15. What is the XMLHTTPRequest object?
Ajax principles

16. Optional values of the Target attribute of the hyperlink: _ blank, _ parent, _ Self, _ top, and framework name. What are the differences between them?

17. What are common JavaScript objects?

String, math, date, and array objects

18. What are the differences between innerhtml, innertext, outerhtml, and innertext?

From: http://qiutian110119.blog.163.com/blog/static/54617311201071751952487/