I wonder if I did something wrong because as far as I know: Object.assign and spread operator will create new object, therefore we can avoid mutate the internal state with is a bad practice. But in my project those two don't seem to work.
First, in my constructor, I setup the state as below:
this.state = {
article: {
title: "",
alias: "",
category: "JAVA",
steps: [
{
stepId: 1,
title: "Dummy title",
description: "The quick brown fox jump over the lazy dog",
length: 30
}
]
},
description: "",
newStep: {
title: "",
length: 0
}
}
Later, I add an addStep() function:
addStep() {
console.log(this.state.article.steps);
let article = { ...this.state.article };
article.steps.push({
stepId: _.last(this.state.article.steps).stepId + 1,
title: this.state.newStep.title,
length: this.state.newStep.length,
description: "",
});
console.log(this.state.article.steps);
}
As you can see this.state.article.steps has been mutated. The same goes for Object.assign. Finally I decide to use and that solved my problem.
let article = JSON.parse(JSON.stringify(this.state.article));
Object.assign{}
and object spread won't deep clone an object.
It will mutate steps
.
It is discussed in the following thread:
let article = { ...this.state.article };
is only making a shallow copy of the object. You can manually make new child keys with something like:
let article = {
...this.state.article,
steps: [...this.state.article.steps]
};
There are many ways to deal with the problem of trying to clone a deeply nested object. This is just one of them.
You could spread the original state this.state.article
and overwrite the nested values (like steps
) with another spread.
let article = {
...this.state.article,
steps: [...this.state.article.steps]
};
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