What does a comma do in JavaScript expressions?
JavascriptComma OperatorJavascript Problem Overview
If I use:
1.09 * 1; // returns "1.09"
But if I use:
1,09 * 1; // returns "9"
I know that 1,09 isn't a number.
What does the comma do in the last piece of code?
More Examples
if (0,9) alert("ok"); // alert
if (9,0) alert("ok"); // don't alert
alert(1); alert(2); alert(3); // 3 alerts
alert(1), alert(2), alert(3); // 3 alerts too
alert("2",
foo = function (param) {
alert(param)
},
foo('1')
)
foo('3'); // alerts 1, 2 and 3
Javascript Solutions
Solution 1 - Javascript
> The comma operator evaluates both of > its operands (from left to right) and > returns the value of the second > operand.
Source: https://developer.mozilla.org/en/JavaScript/Reference/Operators/Special_Operators/Comma_Operator
For example, the expression 1,2,3,4,5
evaluates to 5
. Obviously the comma operator is useful only for operations with side-effects.
console.log(1,2,3,4,5);
console.log((1,2,3,4,5));
Solution 2 - Javascript
Some more to consider:
console.log((0, 9));
console.log((9, 0));
console.log(("foo", "bar"));
Solution 3 - Javascript
Adding/modifying properties to an object and returning it in the same line is a possible use-case:
console.log(
((x) => (o = {biggerCond: r => r >= x},
o.r5 = Array.from(window.crypto.getRandomValues(new Uint16Array(5))),
o.isAnyBigger = o.r5.some(o.biggerCond),
o.bigger = o.isAnyBigger ? o.r5.filter(o.biggerCond) : [x], o )
)(5e4)
);
// Example
// {
// bigger: [58414, 56500, 63397],
// isAnyBigger: true,
// isBiggerCond: r => r >= x,
// r5: [58414, 12015, 56500, 63397, 43861]
// }
The above anonymous function returns an object with random values bigger than the input value or, if there's none, with the input value itself in an array in contained in the bigger
property.
It is still syntactic sugar (like arrow functions), but it does shorten the number of lines... I wonder if some JS minifiers detect and adjust the code in a similar way automatically. Run it in your console:
((x)=>(o={biggerCond:r=>r>=x},o.r5=Array.from(window.crypto.getRandomValues(new Uint16Array(5))),o.isAnyBigger=o.r5.some(o.biggerCond),o.bigger=o.isAnyBigger?o.r5.filter(o.biggerCond):[x],o))(5e4)
Solution 4 - Javascript
The specific syntax allows you to functionally bake bread and hand it to the customer to consume with no return
s.
(new Array(3)).fill()
.map(()=>({state:"dough", bake(){this.state="baked"}, consume(){this.state="consumed"}}))
.map(bread=>(console.log(`Adding ${bread.state} to oven.`), bread.bake(), bread))
.map(bread=>(console.log(`Consuming ${bread.state} bread.`), bread.consume(), bread))
.map(bread=>console.log(`Bread is now ${bread.state}.`))
Adding dough to oven.
Adding dough to oven.
Adding dough to oven.
Consuming baked bread.
Consuming baked bread.
Consuming baked bread.
Bread is now consumed.
Bread is now consumed.
Bread is now consumed.
Solution 5 - Javascript
Have a look [here][1] - the comma stands for multiple expressions / statements. For example in your code you could use a line like this:
var a=0, b=0, c=0;
This would declare all three variables without writing:
var a=0;
var b=0;
var c=0;
Hope that helps. [1]: https://developer.mozilla.org/en/JavaScript/Reference/Operators/Special_Operators/Comma_Operator