ECMAScript 2018 Standard Method
You would use object spread:
let merged = {...obj1, ...obj2};
merged
is now the union of obj1
and obj2
. Properties in obj2
will overwrite those in obj1
.
/** There's no limit to the number of objects you can merge.
* Later properties overwrite earlier properties with the same name. */
const allRules = {...obj1, ...obj2, ...obj3};
Here is also the MDN documentation for this syntax. If you're using babel you'll need the babel-plugin-transform-object-rest-spread plugin for it to work.
ECMAScript 2015 (ES6) Standard Method
/* For the case in question, you would do: */
Object.assign(obj1, obj2);
/** There's no limit to the number of objects you can merge.
* All objects get merged into the first object.
* Only the object in the first argument is mutated and returned.
* Later properties overwrite earlier properties with the same name. */
const allRules = Object.assign({}, obj1, obj2, obj3, etc);
(see MDN JavaScript Reference)
Method for ES5 and Earlier
for (var attrname in obj2) { obj1[attrname] = obj2[attrname]; }
Note that this will simply add all attributes of obj2
to obj1
which might not be what you want if you still want to use the unmodified obj1
.
If you're using a framework that craps all over your prototypes then you have to get fancier with checks like hasOwnProperty
, but that code will work for 99% of cases.
Example function:
/**
* Overwrites obj1's values with obj2's and adds obj2's if non existent in obj1
* @param obj1
* @param obj2
* @returns obj3 a new object based on obj1 and obj2
*/
function merge_options(obj1,obj2){
var obj3 = {};
for (var attrname in obj1) { obj3[attrname] = obj1[attrname]; }
for (var attrname in obj2) { obj3[attrname] = obj2[attrname]; }
return obj3;
}
Do:
var isTrueSet = (myValue === 'true');
using the identity operator (===
), which doesn't make any implicit type conversions when the compared variables have different types.
Don't:
You should probably be cautious about using these two methods for your specific needs:
var myBool = Boolean("false"); // == true
var myBool = !!"false"; // == true
Any string which isn't the empty string will evaluate to true
by using them. Although they're the cleanest methods I can think of concerning to boolean conversion, I think they're not what you're looking for.
Best Answer
Intl.NumberFormat
JavaScript has a number formatter (part of the Internationalization API).
Use
undefined
in place of the first argument ('en-US'
in the example) to use the system locale (the user locale in case the code is running in a browser). Further explanation of the locale code.Here's a list of the currency codes.
Intl.NumberFormat vs Number.prototype.toLocaleString
A final note comparing this to the older .
toLocaleString
. They both offer essentially the same functionality. However, toLocaleString in its older incarnations (pre-Intl) does not actually support locales: it uses the system locale. So when debugging old browsers, be sure that you're using the correct version (MDN suggests to check for the existence ofIntl
). There isn't any need to worry about this at all if you don't care about old browsers or just use the shim.Also, the performance of both is the same for a single item, but if you have a lot of numbers to format, using
Intl.NumberFormat
is ~70 times faster. Therefore, it's usually best to useIntl.NumberFormat
and instantiate only once per page load. Anyway, here's the equivalent usage oftoLocaleString
:Some notes on browser support and Node.js
en-US
out of the box. One solution is to install full-icu, see here for more information