JavaScript string and number conversion

Question

How can I do the following in JavaScript?

1. Concatenate "1", "2", "3" into "123"

2. Convert "123" into 123

3. Add 123 + 100 = 223

4. Covert 223 into "223"

Answer 1

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>