How can I do the following in JavaScript?
Concatenate "1", "2", "3" into "123"
Convert "123" into 123
Add 123 + 100 = 223
Covert 223 into "223"
This question is related to
javascript
string
numbers
You want to become familiar with parseInt() and toString().
And useful in your toolkit will be to look at a variable to find out what type it is—typeof:
<script type="text/javascript">
/**
* print out the value and the type of the variable passed in
*/
function printWithType(val) {
document.write('<pre>');
document.write(val);
document.write(' ');
document.writeln(typeof val);
document.write('</pre>');
}
var a = "1", b = "2", c = "3", result;
// Step (1) Concatenate "1", "2", "3" into "123"
// - concatenation operator is just "+", as long
// as all the items are strings, this works
result = a + b + c;
printWithType(result); //123 string
// - If they were not strings you could do
result = a.toString() + b.toString() + c.toString();
printWithType(result); // 123 string
// Step (2) Convert "123" into 123
result = parseInt(result,10);
printWithType(result); // 123 number
// Step (3) Add 123 + 100 = 223
result = result + 100;
printWithType(result); // 223 number
// Step (4) Convert 223 into "223"
result = result.toString(); //
printWithType(result); // 223 string
// If you concatenate a number with a
// blank string, you get a string
result = result + "";
printWithType(result); //223 string
</script>
You can do it like this:
// step 1
var one = "1" + "2" + "3"; // string value "123"
// step 2
var two = parseInt(one); // integer value 123
// step 3
var three = 123 + 100; // integer value 223
// step 4
var four = three.toString(); // string value "223"
Simplest is when you want to make a integer a string do
var a,b, c;
a = 1;
b = a.toString(); // This will give you string
Now, from the variable b which is of type string we can get the integer
c = b *1; //This will give you integer value of number :-)
If you want to check above is a number. If you are not sure if b contains integer then you can use
if(isNaN(c*1)) {
//NOt a number
}
else //number
r = ("1"+"2"+"3") // step1 | build string ==> "123"
r = +r // step2 | to number ==> 123
r = r+100 // step3 | +100 ==> 223
r = ""+r // step4 | to string ==> "223"
//in one line
r = ""+(+("1"+"2"+"3")+100);
To convert a string to a number, subtract 0. To convert a number to a string, add "" (the empty string).
5 + 1 will give you 6
(5 + "") + 1 will give you "51"
("5" - 0) + 1 will give you 6
parseInt is misfeatured like scanf:
parseInt("12 monkeys", 10) is a number with value '12'
+"12 monkeys" is a number with value 'NaN'
Number("12 monkeys") is a number with value 'NaN'
"1" + "2" + "3"
or
["1", "2", "3"].join("")
The join method concatenates the items of an array into a string, putting the specified delimiter between items. In this case, the "delimiter" is an empty string ("").
parseInt("123")
Prior to ECMAScript 5, it was necessary to pass the radix for base 10: parseInt("123", 10)
123 + 100
(223).toString()
(parseInt("1" + "2" + "3") + 100).toString()
or
(parseInt(["1", "2", "3"].join("")) + 100).toString()
We can do this by using unary plus operator to convert them to numbers first and simply add. see below:-
var a = "4";
var b = "7";
var sum = +a + +b;
Below is a very irritating example of how JavaScript can get you into trouble:
If you just try to use parseInt() to convert to number and then add another number to the result it will concatenate two strings.
However, you can solve the problem by placing the sum expression in parentheses as shown in the example below.
Result: Their age sum is: 98; Their age sum is NOT: 5048
<!DOCTYPE html>_x000D_
<html>_x000D_
<body>_x000D_
_x000D_
<p id="demo"></p>_x000D_
_x000D_
<script>_x000D_
function Person(first, last, age, eye) {_x000D_
this.firstName = first;_x000D_
this.lastName = last;_x000D_
this.age = age;_x000D_
this.eyeColor = eye;_x000D_
}_x000D_
_x000D_
var myFather = new Person("John", "Doe", "50", "blue");_x000D_
var myMother = new Person("Sally", "Rally", 48, "green");_x000D_
_x000D_
document.getElementById("demo").innerHTML = "Their age sum is: "+_x000D_
(parseInt(myFather.age)+myMother.age)+"; Their age sum is NOT: " +_x000D_
parseInt(myFather.age)+myMother.age; _x000D_
</script>_x000D_
_x000D_
</body>_x000D_
</html>These questions come up all the time due to JavaScript's typing system. People think they are getting a number when they're getting the string of a number.
Here are some things you might see that take advantage of the way JavaScript deals with strings and numbers. Personally, I wish JavaScript had used some symbol other than + for string concatenation.
Step (1) Concatenate "1", "2", "3" into "123"
result = "1" + "2" + "3";
Step (2) Convert "123" into 123
result = +"123";
Step (3) Add 123 + 100 = 223
result = 123 + 100;
Step (4) Convert 223 into "223"
result = "" + 223;
If you know WHY these work, you're less likely to get into trouble with JavaScript expressions.
Source: Stackoverflow.com