https://facebook.github.io/re...handleClick(i) {    const squares = this.state.squares.slice();     squares[i] = 'X';    this.setState({squares: squares});   }Determining if a mutated object has changed is complex because changes are made directly to the object. This then requires comparing the current object to a previous copy, traversing the entire object tree, and comparing each variable and value. This process can become increasingly complex.Determining how an immutable object has changed is considerably easier. If the object being referenced is different from before, then the object has changed. That's it.以上摘自React的引導(dǎo), 有個關(guān)于slice()的疑問: 為什么要復(fù)制一份數(shù)據(jù)呢? 使用slice()復(fù)制出來的數(shù)據(jù)對比差異還是要全部遍歷