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64. What's the output? const value = { number: 10 }; const multiply = (x = { ...value }) => { console.log((x.number *= 2)); }; multiply(); multiply(); multiply(value); multiply(value);
Output?
Anonymous Poll
33%
A: 20, 40, 80, 160
0%
B: 20, 40, 20, 40
50%
C: 20, 20, 20, 40
17%
D: NaN, NaN, 20, 40
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Output?
Answer: C
In ES6, we can initialize parameters with a default value. The value of the parameter will be the default value, if no other value has been passed to the function, or if the value of the parameter is "undefined". In this case, we spread the properties of the value object into a new object, so x has the default value of { number: 10 }.
The default argument is evaluated at call time! Every time we call the function, a new object is created. We invoke the multiply function the first two times without passing a value: x has the default value of { number: 10 }. We then log the multiplied value of that number, which is 20.
The third time we invoke multiply, we do pass an argument: the object called value. The *= operator is actually shorthand for x.number = x.number * 2: we modify the value of x.number, and log the multiplied value 20.
The fourth time, we pass the value object again. x.number was previously modified to 20, so x.number *= 2 logs 40.
In ES6, we can initialize parameters with a default value. The value of the parameter will be the default value, if no other value has been passed to the function, or if the value of the parameter is "undefined". In this case, we spread the properties of the value object into a new object, so x has the default value of { number: 10 }.
The default argument is evaluated at call time! Every time we call the function, a new object is created. We invoke the multiply function the first two times without passing a value: x has the default value of { number: 10 }. We then log the multiplied value of that number, which is 20.
The third time we invoke multiply, we do pass an argument: the object called value. The *= operator is actually shorthand for x.number = x.number * 2: we modify the value of x.number, and log the multiplied value 20.
The fourth time, we pass the value object again. x.number was previously modified to 20, so x.number *= 2 logs 40.
65. What's the output?
[1, 2, 3, 4].reduce((x, y) => console.log(x, y));
[1, 2, 3, 4].reduce((x, y) => console.log(x, y));
Anonymous Poll
13%
A: 1 2 and 3 3 and 6 4
19%
B: 1 2 and 2 3 and 3 4
19%
C: 1 undefined and 2 undefined and 3 undefined and 4 undefined
50%
D: 1 2 and undefined 3 and undefined 4
https://thedailyfrontend.com/how-to-create-html-elements-dynamically-and-bind-events-with-javascript/
Let's learn in detail 😌
How to Create HTML Elements Dynamically and Bind Events with JavaScript
Let's learn in detail 😌
How to Create HTML Elements Dynamically and Bind Events with JavaScript
The Daily Frontend
How to Create HTML Elements Dynamically and Bind Events with JavaScript - The Daily Frontend
Learn how to Create HTML Elements Dynamically and Bind Events with JavaScript step by step in this article.
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65. What's the output?
[1, 2, 3, 4].reduce((x, y) => console.log(x, y));
[1, 2, 3, 4].reduce((x, y) => console.log(x, y));
Answer: D
The first argument that the reduce method receives is the accumulator, x in this case. The second argument is the current value, y. With the reduce method, we execute a callback function on every element in the array, which could ultimately result in one single value.
In this example, we are not returning any values, we are simply logging the values of the accumulator and the current value.
The value of the accumulator is equal to the previously returned value of the callback function. If you don't pass the optional initialValue argument to the reduce method, the accumulator is equal to the first element on the first call.
On the first call, the accumulator (x) is 1, and the current value (y) is 2. We don't return from the callback function, we log the accumulator and current value: 1 and 2 get logged.
If you don't return a value from a function, it returns undefined. On the next call, the accumulator is undefined, and the current value is 3. undefined and 3 get logged.
On the fourth call, we again don't return from the callback function. The accumulator is again undefined, and the current value is 4. undefined and 4 get logged.
The first argument that the reduce method receives is the accumulator, x in this case. The second argument is the current value, y. With the reduce method, we execute a callback function on every element in the array, which could ultimately result in one single value.
In this example, we are not returning any values, we are simply logging the values of the accumulator and the current value.
The value of the accumulator is equal to the previously returned value of the callback function. If you don't pass the optional initialValue argument to the reduce method, the accumulator is equal to the first element on the first call.
On the first call, the accumulator (x) is 1, and the current value (y) is 2. We don't return from the callback function, we log the accumulator and current value: 1 and 2 get logged.
If you don't return a value from a function, it returns undefined. On the next call, the accumulator is undefined, and the current value is 3. undefined and 3 get logged.
On the fourth call, we again don't return from the callback function. The accumulator is again undefined, and the current value is 4. undefined and 4 get logged.