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Start your free trialJanaka Bandara
1,329 PointsWhen you store seconds in a const, how come that value gets changed? Isn't const an immutable (for primitive) in ES2015?
In this video, when the teacher wanted to calculate the time in seconds, he declared a const second in render method. Now in previous ES2015 tutorials, it says when you declare a variable as const and if it holds a primitive data type, that variable is immutable. JS suppose to give you a warning, but in React this doesn't happens. Any idea why?
Thanks
3 Answers
Daniel Totten
Full Stack JavaScript Techdegree Graduate 21,008 PointsIf I'm understanding this all correctly, I think the render() method gets called every time there is a state change. Therefore, the seconds variable is created each time the render() method is called, not updated, and therefore is still immutable. I think if we put the seconds variable in a different scope, we would have to use let instead of const.
Kevin Nguyen
1,317 PointsNot sure what you need, but it can be:
const obj = {}
We can't change it, but we can modify its parameters like:
// Allowed
obj.name = 'me'
// Not allow
var obj = {
name: 'me'
}
Janaka Bandara
1,329 PointsHi thanks for the reply, But in the video (~1:30 mins)
const seconds = Math.floor(this.state.elapsedTime / 1000);
This is a number type . So it should not get changed right?
Nicopixel Nicopixel
Courses Plus Student 91 PointsThe variables declared with "const" and "let" are "scopped", means that "seconds" doesn't exits outside any scope http://es6-features.org/#BlockScopedVariables
Janaka Bandara
1,329 PointsJanaka Bandara
1,329 PointsGot it, I missed that completely. Thanks Daniel