which one is correct? alert((+"123")) alert(+"123") alert(+("123"))

Question

I'm trying to convert a string to a float. I know that parseFloat() can do that, but I've also found the syntax below, but without much reference.

What is the correct syntax, because they all seem to work. And where can I learn more about it? I don't know how to Google it, because I don't know what it's named.

// syntax 1
alert((+"123"));    // 123
alert((+"x123"));   // NaN
alert((+"123x"));   // NaN
alert((+"123   ")); // 123
alert((+"   123")); // 123
alert((+"12 3"));   // NaN

// syntax 2
alert(+"123");      // 123
alert(+"x123");     // NaN
alert(+"123x");     // NaN
alert(+"123   ");   // 123
alert(+"   123");   // 123
alert(+"12 3");     // NaN

// syntax 3
alert(+("123"));    // 123
alert(+("x123"));   // NaN
alert(+("123x"));   // NaN
alert(+("123   ")); // 123
alert(+("   123")); // 123
alert(+("12 3"));   // NaN

The extra `( )` don't do anything special here, because they are just grouping a single computed value (syntax 1) or literal (syntax 3), and the meaning is no different if you remove the `( )`. If you were to do something like `alert(+("123" + "456"));`, then the extra `( )` would be doing something meaningful, and the computation would change with their removal (although the result would end up being the same, but the way in which you get there would not be). — ajp15243, Apr 24 '13 at 14:33
Also, [this question about JavaScript unary operators](http://stackoverflow.com/questions/12120802/explain-var-and-var-unary-operator-in-javascript) may help answer your question. — ajp15243, Apr 24 '13 at 14:36

score 3 · Answer 1 · answered Apr 24 '13 at 14:26

3

They're all syntactically correct...but examples 1 and 3 have redundant brackets.

answered Apr 24 '13 at 14:26

Andreas Grech

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score 2 · Accepted Answer · answered Apr 24 '13 at 14:29

2

This is called implicit conversion. Since you used a mathematical operator (+), it tries to convert the string to a numeric value which is needed for mathematical operations. What you are asking here is give me the positive value of the following string.

answered Apr 24 '13 at 14:29

Dominic Goulet

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thank you, except that I don't find it to return a positive value – wubbewubbewubbe Apr 24 '13 at 14:41
+1 for mentioning implicit conversion, but I prefer the term `coercion` because it sounds cooler :) – Andreas Grech Apr 24 '13 at 14:55
@wubbewubbewubbe Is not `123` the positive value of `"123"` ? – Dominic Goulet Apr 24 '13 at 14:59
I'm not sure what you mean, try alert(+"-123"); // -123 – wubbewubbewubbe Apr 24 '13 at 15:02
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@wubbewubbewubbe: the unary `+` operator in JavaScript has nothing to do with returning the positive value of a number; if you want to do that, use `Math.abs(+"-123");`. – Andreas Grech Apr 24 '13 at 15:04
You are absolutely right. I was not referring to absolute value though, simply positive representation. In my head, the positive representation of a negative number is still negative, but that was poorly explained / outlined in my answer. – Dominic Goulet Apr 24 '13 at 15:09

which one is correct? alert((+"123")) alert(+"123") alert(+("123"))

2 Answers2