Very simple JavaScript code doesn't work?
Question
I'm a beginner on JavaScript so can someone tell me why this doesn't work?
<!doctype html>
<head>
<title>Assignment</title>
</head>
<script>
var name = ("John" & "Penny" & "Pat")
name = prompt("What is the student name?");
if (name="John" && "Penny" && "Pat")
{
document.write(name + " has one free hour of lessons.");
}
else
{
document.write(name + "doesn't have any free lessons.");
}
</script>
It will prompt me with the question but despite what I input it will always output with "Pat has one free hour of lessons." Anyone help me?
4 answers
solution1
4 2014-04-02 18:10:33
You're using the wrong equals here:
if (name="John" && "Penny" && "Pat")
Change it to
if (name === "John" || name === "Penny" || name === "Pat")
You're also setting name incorrectly:
var name = ("John" & "Penny" & "Pat")
should be
var name = ["John", "Penny", "Pat"];
(if you want an array.) (Though you're overwriting it in the next line, so why ever set it like that in the first place?).
Finally, it's bad practice to use document.write , try console.log instead.
To sum up so far:
var name = prompt("What is the student name?");
if (name === "John" || name === "Penny" || name === "Pat") {
console.log(name + " has one free hour of lessons.");
} else {
console.log(name + " doesn't have any free lessons.");
}
As noted in the comments, this gets difficult when you add more users. Instead, let's store the users who have a free hour in an array (thus, adding new students is easy, just add them to the array):
var haveFreeHour = ["John", "Penny", "Pat"];
Then, we can use indexOf in the if statement:
var haveFreeHour = ["John", "Penny", "Pat"];
var name = prompt("What is the student name?");
if (haveFreeHour.indexOf(name) > -1) {
console.log(name + " has one free hour of lessons.");
} else {
console.log(name + " doesn't have any free lessons.");
}
solution2
0 2014-04-02 18:12:41
You need to use == or === for comparison.
Here is more info on what each one does http://www.2ality.com/2011/06/javascript-equality.html
Strict equals === [ES5 11.9.6] Comparing two values. Values with different types are never equal. If both values have the same type then the following assertions hold.
Equals == [ES5 11.9.3] Comparing two values. If both values have the same type: compare with ===. Otherwise: undefined == null One number, one string: convert the string to a number A boolean and a non-boolean: convert the boolean to a number and then perform the comparison. Comparing a string or a number to an object: try to convert the object to a primitive and then make the comparison.
Also your names variable should be used as an Array and a different one for your prompt, something like :
var names = ["John", "Penny", "Pat"];
var name = prompt("What is the student name?");
Then instead of comparison you could use indexOf ( more on indexOf) to see if your value is in your array, something like :
if(names.indexOf(name) > -1)...
solution3
0 2014-04-02 18:20:42
Here's what you want:
<!DOCTYPE html>
<head>
<title>Assignment</title>
</head>
<body>
<script type="text/javascript">
var names = ["John","Penny","Pat"];
var name = prompt("What is the student name?");
if(names.indexOf(name) > -1)
{
console.log(name + " has one free hour of lessons.");
}
else
{
console.log(name + " doesn't have any free lessons.");
}
</script>
</body>
</html>
PS You should avoid using document.write. I have edited the code and changed that part to console.log
solution4
-3 2014-04-02 18:09:55
您需要对条件使用双== 。
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