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I have troubles understanding the meaning of (_,idx) in the following statement
arr.filter((_, idx) => idx % 2 === 0)
I understand it is filtering the array and just returning on the new array all elements that respect the condition(basically with even index). But i do not understand what this (_,idx) means?
Any help?
(_, idx) are two variable names.
arr.filter((currentValue, index, array) => )
As you can read here.
So "_" is currentValue and "idx" is the index.
"_" is not use but still defindes because it is a non-optional parameter, so you always have to give it an name.
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I have explore a few webs and watch some videos but I couldn't understand how array.forEach() works
This is the script that I found regarding that
let meals = ["rice", "meat", "salad"];
meals.forEach(capitalize);
meals.forEach(print);
function capitalize(element, index, array){
array[index] = element[0].toUpperCase() + element.substring(1);
}
function print(element){
console.log(element);
}
Can someone explain to me about how array[index] = element(0).toUpperCase() + element.substring(1); and meal.forEach(); works?
forEach() is an array function from JavaScript, that is used to iterate over items in a given array.
element[0] will return first character of each array element.
toUpperCase() is function use to convertthe string into upper case.
element.substring(1) this will return a string, except for the first character.
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I face an issue with a so simple js transformation !
Here is my array
["one", "two"]
Here is what I want to output
["en/one", "en/one", "fr/two", "fr/two"]
What I'm trying to do with my knowledge
let a = ["one", "two"];
let b = a.map(x => `en/${x}`,`fr/${x}`);
console.log(b);
But I get an error:
ReferenceError: x is not defined
How can I make this work?
The way you wrote it, `fr/${x}` becomes a second argument to .map() (where x is not in scope). You need to combine the two values in an array...
And then you can use flatMap:
let b = a.flatMap(x => [`en/${x}`,`fr/${x}`]);
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I have been asked to show I have used these processes in my program but from looking up the definitions, I don't know what they mean. I am confident my program is complicated enough that it uses these processes, but I don't know exactly what they are. What would be an example of these processes used in javascript?
Unsure what you mean by custom function - but recursion is just a function that calls itself.
Example of recursion
countNumTimesToZero = (myNum, count = 0) => {
if (myNum - 1 === 0) return count + 1;
return countNumTimesToZero(myNum - 1, count + 1);
}
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I have an array like this:
var animals=["cat","dog","snake","rhino"];
But sometimes I have to delete this array(remove it from the dom).
I have tried animals.remove; and $(animals).remove() and animals.remove() but none of them did the trick.Any ideas?
var animals=["cat","dog","snake","rhino"];
then to clear it do:
animals=[];
or
animals.length=0;
or
while(animals.length > 0) {
animals.pop();
}
Just assign the animals array to a value undefined and the array data will be dereferenced and garbage collected.
Donot try to call delete operator that is explicit removal.
animals = undefined
OR
animals = void 0
Thanks
Just Clear The Array
Using This 2 Methods
animals.length =0
animals=[];
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Hi this is a simple question. I was wondering is there any different when you declare something like this. Thanks
selectedData[key](val)
and
selectedData[key] = val
This line selectedData[key](val) is not a declaration, it's calling the function that is stored under the key key in the object selectedData and it's passing the parameter val to that function.
The other line selectedData[key] = val is assigning the value val to the key key in the object selectedData.
In the first case, you're calling whatever is in selectedData[key] as a function with val as an argument while in the second one you're assigning it.