I want to convert an array to string in NodeJS.
var aa = new Array();
aa['a'] = 'aaa';
aa['b'] = 'bbb';
console.log(aa.toString());
But it doesn't work.
Anyone knows how to convert?
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5 Answers
You're using an Array like an "associative array", which does not exist in JavaScript. Use an Object ({}) instead.
If you are going to continue with an array, realize that toString() will join all the numbered properties together separated by a comma. (the same as .join(",")).
Properties like a and b will not come up using this method because they are not in the numeric indexes. (ie. the "body" of the array)
In JavaScript, Array inherits from Object, so you can add and delete properties on it like any other object. So for an array, the numbered properties (they're technically just strings under the hood) are what counts in methods like .toString(), .join(), etc. Your other properties are still there and very much accessible. :)
Read Mozilla's documentation for more information about Arrays.
var aa = [];
// these are now properties of the object, but not part of the "array body"
aa.a = "A";
aa.b = "B";
// these are part of the array's body/contents
aa[0] = "foo";
aa[1] = "bar";
aa.toString(); // most browsers will say "foo,bar" -- the same as .join(",")
Comments
toString is a method, so you should add parenthesis () to make the function call.
> a = [1,2,3]
[ 1, 2, 3 ]
> a.toString()
'1,2,3'
Besides, if you want to use strings as keys, then you should consider using a Object instead of Array, and use JSON.stringify to return a string.
> var aa = {}
> aa['a'] = 'aaa'
> JSON.stringify(aa)
'{"a":"aaa","b":"bbb"}'
2 Comments
Magic
Type mistake for the parenthesis. It's corrected. Can you explain why use Object for the string as keys. Why Array can't not be use? And why Object.toString() not work?
qiao
@Magic see this great post: andrewdupont.net/2006/05/18/…
toString is a function, not a property. You'll want this:
console.log(aa.toString());
Alternatively, use join to specify the separator (toString() === join(','))
console.log(aa.join(' and '));
Comments
In node, you can just say
console.log(aa)
and it will format it as it should.
If you need to use the resulting string you should use
JSON.stringify(aa)
2 Comments
Magic
JSON.stringify(aa) can't print the content. Because my array is string index. It only work for int index array.
Tor Valamo
@Magic - There's no such thing as a string index array in js. The only reason aa['a'] works is because the Array type inherits from Object, so it will emulate an associative array, while in fact a lot of the array functions will no longer work because of it, and there are other pitfalls. If you need associative array, you should use an object
{a:0, b:4} instead of the array type, which only really works on numeric indexes [0,4]You can also cast an array to a string like...
newStr = String(aa);
I also agree with Tor Valamo's answer, console.log should have no problem with arrays, no need to convert to a string unless you're debugging something or just curious.
