What's the difference between
"2" * 1 + 5
and
parseInt("2") + 5
It's just a to write a more readable code, or there are compatibility issues with the first form.
2 Answers
parseInt is used to grab integers from a string. Consider the following code:
var myString = "3 blind mice";
var myInteger = parseInt(myString); //3
JavaScript will do automatic type conversion, so something like this:
"2" * 1 + 5 //7
The string "2" gets converted to a number.
As noted above in the comments, parseInt takes an additional argument for the base.
JavaScript has a lot of very weird rules about type conversion, and sometimes it's not exactly clear what JavaScript will do in every situation. Keep in mind that the + operator is also used for concatenation as well as addition.
If you're trying to explicitly convert something to a number, you can use the Number constructor provided by JavaScript. Considering the following:
var myString = "2";
var myNum = Number(myString); //2
console.log(typeof myNum); //number
Without the new keyword, it can be used to convert strings to numbers. While it does work, I am not sure parseInt should be used for conversion. Just use the Number constructor.
5 Comments
Sir
"2" + 1 + 5 does not equal 8 it equals 215
phenomnomnominal
I think you mean
"2" * 1 + 5 // 7 as "2" + 1 + 5 will print 215.
Sethen
Yup! That's what I mean. Small typo, my bad.
Sir
"2" * 1 + 5 //8 is 7 :PSethen
I messed that up, my bad. I fixed it.
I don't think there are compatibility issues with using coercion in the first form, it is a language feature that should be widely supported.
However, since you have to add code to do the conversion either way (* 1 vs. parseInt), I would vote for parseInt from a style perspective because it makes your intention clearer. It is hard enough sometimes to keep types straight in javascript without using implicit conversions.
Someone not familiar with your code or with javascript might wonder what is going on with that first form as well.
Plus, as indicated in the comments, parseInt is faster so it's a win all around.
25not7parseInt()optionally takes 2 parameters, the second being the "radix" (or "base") the input is in. If omitted, and the input begins with a0, the base is defaulted to octal (or base-8) which will give undesired results. So, there is at least a side-effect to using the latter in the way you do in your example; a more appropriate way would beparseInt("2", 10)*is not related to strings so it can only mean mathematical function