JS implementation to check whether an array object contains values from another array object

  // Two array objects   Whether one of the array objects contains values from the other array object 
      let arr = [
        {key:1,val:" Zhang Shengnan "},
        {key:2,val:" Wang Wu "},
        {key:3,val:" Li Si "},
        {key:4,val:" Liu chao "},
        {key:5,val:" Zhao si "}
      ]
      let arr2 = [
        {key:1,val:" Zhang Shengnan "},
        {key:2,val:" Wang Wu "},
       {key:6,val:"666"},
       {key:7,val:"777"},
       {key:8,val:"888"},
       {key:9,val:"999"},
      ]
      // If it can be found, the corresponding subscript will be returned , If you can't find it , Just go back to -1
      for(let i=0;i<arr.length;i++){
        const Index = arr2.findIndex((item) => {return item.key === arr[i].key})
        console.log(Index);  // 0、1、-1、-1、-1
        //  Of the first two data key Same value , Print out the corresponding subscript  , Find something different in the back key   Output -1
      }

  // Two array objects   Whether one of the array objects contains values from the other array object 
      let arr = [
        {key:1,val:" Zhang Shengnan "},
        {key:2,val:" Wang Wu "},
        {key:3,val:" Li Si "},
        {key:4,val:" Liu chao "},
        {key:5,val:" Zhao si "}
      ]
      let arr2 = [
        {key:1,val:" Zhang Shengnan "},
        {key:2,val:" Wang Wu "},
       {key:6,val:"666"},
       {key:7,val:"777"},
       {key:8,val:"888"},
       {key:9,val:"999"},
      ]
      
      for(let task of arr){
        const itemJson = arr2.find((item)=>{return item.key === task.key});
        console.log(itemJson)
        //{key: 1, val: " Zhang Shengnan "}
        //{key: 2, val: " Wang Wu "}
        // 3 undefined
       //  If there is the same value, the corresponding object is returned   If not, return  undefined
       }

Both of the above methods can find Whether an array object contains elements from another array object , The two methods return different results , One is the return subscript , In addition, the corresponding object is returned , In the actual application scenario, different usage modes can be selected according to different needs .