Native deep cloning
It's called "structured cloning", works experimentally in Node 11 and later, and hopefully will land in browsers. See this answer for more details.
Fast cloning with data loss - JSON.parse/stringify
If you do not use Date
s, functions, undefined
, Infinity
, RegExps, Maps, Sets, Blobs, FileLists, ImageDatas, sparse Arrays, Typed Arrays or other complex types within your object, a very simple one liner to deep clone an object is:
JSON.parse(JSON.stringify(object))
const a = {
string: 'string',
number: 123,
bool: false,
nul: null,
date: new Date(), // stringified
undef: undefined, // lost
inf: Infinity, // forced to 'null'
re: /.*/, // lost
}
console.log(a);
console.log(typeof a.date); // Date object
const clone = JSON.parse(JSON.stringify(a));
console.log(clone);
console.log(typeof clone.date); // result of .toISOString()
See Corban's answer for benchmarks.
Reliable cloning using a library
Since cloning objects is not trivial (complex types, circular references, function etc.), most major libraries provide function to clone objects. Don't reinvent the wheel - if you're already using a library, check if it has an object cloning function. For example,
- lodash -
cloneDeep
; can be imported separately via the lodash.clonedeep module and is probably your best choice if you're not already using a library that provides a deep cloning function
- AngularJS -
angular.copy
- jQuery -
jQuery.extend(true, { }, oldObject)
; .clone()
only clones DOM elements
- just library -
just-clone
; Part of a library of zero-dependency npm modules that do just do one thing.
Guilt-free utilities for every occasion.
ES6 (shallow copy)
For completeness, note that ES6 offers two shallow copy mechanisms: Object.assign()
and the spread syntax.
which copies values of all enumerable own properties from one object to another. For example:
var A1 = {a: "2"};
var A2 = Object.assign({}, A1);
var A3 = {...A1}; // Spread Syntax
If you just want to check whether there's a truthy value, you can do:
if (strValue) {
//do something
}
If you need to check specifically for an empty string over null, I would think checking against ""
is your best bet, using the ===
operator (so that you know that it is, in fact, a string you're comparing against).
if (strValue === "") {
//...
}
Best Answer
2nd October 2020: note that many bare-bones approaches are fraught with subtle bugs (eg. whitespace, implicit partial parsing, radix, coercion of arrays etc.) that many of the answers here fail to take into account. The following implementation might work for you, but note that it does not cater for number separators other than the decimal point "
.
":To check if a variable (including a string) is a number, check if it is not a number:
This works regardless of whether the variable content is a string or number.
Examples
Of course, you can negate this if you need to. For example, to implement the
IsNumeric
example you gave:To convert a string containing a number into a number:
Only works if the string only contains numeric characters, else it returns
NaN
.Examples
To convert a string loosely to a number
Useful for converting '12px' to 12, for example:
Examples
Floats
Bear in mind that, unlike
+num
,parseInt
(as the name suggests) will convert a float into an integer by chopping off everything following the decimal point (if you want to useparseInt()
because of this behaviour, you're probably better off using another method instead):Empty strings
Empty strings may be a little counter-intuitive.
+num
converts empty strings or strings with spaces to zero, andisNaN()
assumes the same:But
parseInt()
does not agree: