This question already has answers here:
Why can't I access a property of an integer with a single dot?
(5 answers)
Closed 4 years ago.
I guess that javascript will parse (2).valueOf() to new Number(2).valueOf() but why it doesn't for the first one ?
According to the operator precedence, the grouping operator shall have a higher priority than the member access https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/Operator_Precedence
So why (2) is not be evaluated first and yield 2 instead of be parsed to new Number(2) ?
Because in 2.valueOf the . is considered to be as a part of 2 instead of being understood as method accessing.
That is why 2..valueOf() works.
console.log(2..valueOf());
Related
This question already has answers here:
do loose equality comparision using array.includes
(2 answers)
How does the Array.prototype.includes function compare objects
(5 answers)
Closed 4 months ago.
While writing a sudoku solver, I ran into a issue which took me hours to solve which is based on ['1','2','3'].includes(3). is false. Since 3 in includes is a type number but 3 in array is type string. But this is against the intuition that type coercion happens while comparing values in js? Should it be corrected in js?
ex: ['1','2','3'].includes(3) // false
and ['1','2','3'].includes('3') // true
Throw some light on whether this is needed or should be fixed as it will lead to errors in programs if not checked carefully.
This question already has answers here:
When is the comma operator useful?
(15 answers)
Closed 1 year ago.
I have the following:
let currentLocalStorage = [];
currentLocalStorage = (initialLoad) ? JSON.parse(localStorage.getItem('tasks')): (currentLocalStorage.push(taskInput.value),currentLocalStorage)
which works but I would like to get a reference or documentation for the following:
: (currentLocalStorage.push(taskInput.value),currentLocalStorage)
so basically we are pushing on to the array and then defaulting to the array. I was surprised that we can do this and was wondering where one we look for the documentation
This is using the comma operator. Because .push() returns the new length of the array, you want to make sure you don't assign that to currentLocalStorage, so you use the comma operator to have that expression evaluate to currentLocalStorage.
So it effectively becomes currentLocalStorage = currentLocalStorage in that case, except now the array has one more item thanks to .push().
This question already has answers here:
Why can't I access a property of an integer with a single dot?
(5 answers)
Calling member function of number literal
(3 answers)
Closed 2 years ago.
Is this means assignment in js of primitive makes primitive become object automatically?
let a = 1 just be transferred to let a = new Number(1), we know Number is a function, and it's prototype has toString, this makes sense? Is it right?
Finally, we know the primitive of js is stored in stack memory, but if we can only get object by assignment, so is it means only pointer exists in stack? I am confused. Thanks for your answers if you can help me.
You can not call Number.prototype methods directly from a number in digits form, e.g. 1 2 3 4 5 6 7 8 9, you have to wrap them in parentheses.
// This doesn't work
console.log(1.toString());
// This works
console.log((1).toString());
This question already has answers here:
What "..." means in Javascript (ES6)? [duplicate]
(1 answer)
Spread Syntax vs Rest Parameter in ES2015 / ES6
(11 answers)
Closed 4 years ago.
I’m new to coding and slef teaching JavaScript.
My task I was set was to identify the largest value in an array.
My soloition works, but I needed the ‘...’ for it to work properly.
My question is, what does the ‘...’ in the last line actually mean/do?
function createAnArr(){
let myArr = prompt("Enter your numbers separated by commas:").split(",");
return myArr;
}
console.log(Math.max(...createAnArr()));
'...' it means it will be able to take any number of arguments of the respective scope
'...': The spread operator is used for array construction and destructuring, and to fill function arguments from an array on invocation. A case when the operator spreads the array (or iterable object) elements.
more details you can see here
This question already has answers here:
Javascript if in x [duplicate]
(3 answers)
Closed 6 years ago.
Hi i'm following a tutorial learning to use javascript.
function move(keyclick) {
if(40 in keyclick) {}
playerMove.x++;
render(); }
What does the 'in' word mean? I understand what the function is doing, but why not just use ==
?
Thanks
The in operator is true if the string on the LHS is the name of a property that exists on the object on the RHS.
== tests if a value matches another value, which is entirely different.
The in operator returns true if the specified property is in the specified object (cited from https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Operators/in).