对数组

Question

我有点卡住了。我尝试使用另一个数组中的另一个对象覆盖数组中的某个对象：

onStepsLayoutChange = (layout) => {
        console.log("The new layout is", layout); //Array
        this.setState((prevState) => ({
            layout: layout,
            stepsData: prevState.stepsData.map(step => {
                layout.map(l => {
                  if(step.identifier === parseInt(l.i)){
                      console.log("Match", l, step); // "l" is not empty and actually matches only if "id" is identical
                      return {
                          ...step,
                          layout: l //I want to override "layout" with the current layout "l"
                      }
                  }
                });
                return step
            })
        }), () => console.log("LayoutChange:", this.state.layout, this.state.stepsData)); // "layout" in each step is empty
    };

在这种情况下，我的失败是什么？

Answer 1

如果stepsData必须是数组数组，则会忘记返回：

onStepsLayoutChange = (layout) => {
        console.log("The new layout is", layout); //Array
        this.setState((prevState) => ({
            layout: layout,
            stepsData: prevState.stepsData.map(step => {
                return layout.map(l => { //here <---
                  if(step.identifier === parseInt(l.i)){
                      console.log("Match", l, step); // "l" is not empty and actually matches only if "id" is identical
                      return {
                          ...step,
                          layout: l //I want to override "layout" with the current layout "l"
                      }
                  }
                });
                return step
            })
        }), () => console.log("LayoutChange:", this.state.layout, this.state.stepsData)); // "layout" in each step is empty
    };

Answer 2

问题是，您缺少#array.map的默认行为。对于每个数组值，映射将默认返回一些值undefined。你正在map中运行map，所以stepData的最终值是：

[[...], [...], [....] ....]

不使用嵌套地图，而是使用#array.findIndex或#array.find并返回值。

像这样写：

stepsData: prevState.stepsData.map(step => {
    let index;
    index = layout.findIndex(l => step.identifier === parseInt(l.i));

    if(index >= 0){
        return {
            ...step,
            layout: layout[index]
        }
    }

    return step;
})

检查此代码段：

let a = [1,2,3,4,5];
let b = [2,3];

let result = a.map(i => {
   return b.map(j => {
      if(i === j)
         return 0;
   })
   return i;
})

console.log(result);