问题
This is a question I've been wondering about ever since I found the toString() function, but have never bothered to ask. Should I use basic JS or the function that does the same thing?
Now, don't get me wrong, I realize toString has its redeeming qualities, like converting a function to a string.
var message = function() {
// multi
// line
// string
}.toString();
But admit it: we mainly use toString for converting numbers to strings. Couldn't we just do this instead?
var myNumber = 1234;
var message = ''+myNumber;
Not only is this shorter, but according to JSPerf the toString method is 97% slower! (Proof: http://jsperf.com/tostring-vs-basic-js ) And as I said, I know toString is useful, but when people raise question about types of Javascript variables, toString() usually comes up. And this is, like, basic Javascript. Every browser can do quotes.
Same goes for parseInt. Now, before I discovered parseInt, I discovered that multiplying a string by one would convert it to a number. That's because you cannot multiply a string, naturally, forcing Javascript to treat it as a number.
var message = "4321";
var myNumber = message*1;
Now, interestingly, this is slower than parseInt, but not by much. I also noticed that an empty string, or one without numbers, will return 0, whereas parseInt will return NaN because there are no numbers in the string. Once again, I realize parseInt is faster and can convert to different bases. However, multiplying is shorter, will work in any browser, and parseInt, remember, will only return integers. So why does it always come up as the answer to questions, asking how to convert to numbers/what NaN is?
Now this might be going a little bit off topic, but I actually wonder a similar thing about jQuery. Once again, jQuery is something I've never really understood the use for. Javascript code is clean and jQuery is in and of itself a JS file, so it cannot do anything Javascript can't do. It may simplify certain functions and stuff, but why not just copy those functions to your page then and leave out the remaining functions you don't use? It seems overkill to include jQuery merely to complete one simple task. And animation isn't excused either here - because that too can be done with native Javascript. So why jQuery?
Ultimately what I'm asking is, why do we need these things for these purposes when there are better methods? Or are they better methods? Is using functions a better practive just in general?
回答1:
Not only is this shorter, but according to JSPerf the toString method is 97% slower!
Unless you're calling .toString() on hundreds of millions of numbers every second and you've found that this is a bottleneck in your application through profiling, this should not be a factor at all.
But admit it: we mainly use toString for converting numbers to strings
As you've seen, this can be done implicitly by just adding a string and a number together, so I fail to see any benefit of using '' + n in place of n.toString(). The latter is more readable when you're not actually concatenating n with a string.
However, multiplying is shorter, will work in any browser, and parseInt, remember, will only return integers.
Are you saying that parseInt doesn't work in every browser? If you want to parse something as an integer, use parseInt. If you want to parse something as a float (JavaScript doesn't actually have a special type for either, all numbers are floats), use parseFloat.
The more common pattern is using +'123', which has the exact same behavior as 1 * '123'. parseInt handles empty strings properly, but for whatever reason does not validate strings as you'd expect. The unary plus returns NaN in case of an error, but treats whitespace and empty strings incorrectly. It's one of JavaScript's shortcomings, so there's really no concrete choice between the two if you're working in base 10.
So why does it always come up as the answer to questions, asking how to convert to numbers/what NaN is?
Because the spec included these functions to convert strings into numbers and converting strings into numbers using binary operators like you're doing is a side effect, not the primary purpose. Also you can parse integers in different bases using parseInt, which isn't possible with type coercion.
It may simplify certain functions and stuff, but why not just copy those functions to your page then and leave out the remaining functions you don't use?
If you load jQuery from a CDN, then there's a really good chance that a user's browser has already downloaded it and has it cached, making download times and bloat almost nonexistent. If you make a "custom build", I'd bet that it'll make the site slower on first load.
And animation isn't excused either here - because that too can be done with native Javascript.
So can everything. There's no point in reinventing the wheel every time you write something.
来源：https://stackoverflow.com/questions/23879341/method-vs-basic-js-should-i-use-tostring-parseint-jquery