The method of array traversal in JS

foreach

• Traversal array , Once started, it cannot be stopped
• Parameters can be two , A value representing each element , The other of the two represents index Value , You can also pass in other parameters to be placed in the following

<script> const arr = [' Xiaohong ',' bright red ',' Su Daqiang ',' Baby '] // foreach Once you start, you can't stop in the middle  arr.forEach((item,index)=>{
       console.log(item + '======' + index); if(item == ' Su Daqiang '){
       console.log(' Su Daqiang's index number ：'+ index); } }) </script>

some

• After the start After the conditions are met, you can pass return true To end the traversal

<script> // some After finding the index return true The fixed writing method will not be executed later  arr.some((item,index)=>{
       console.log(item + '======' + index); if(item == ' Su Daqiang '){
       console.log(' Su Daqiang's index number ：'+ index); return true } }) </script>

every

• There is a return value
• Judge whether the conditions are met , If any item does not meet the conditions, it will return to false

<script> const arr1 = [ {
      id:1 , name:' watermelon ', state:true}, {
      id:2 , name:' durian ', state:false}, {
      id:3 , name:' strawberry ', state:true} ] //  Judge whether the conditions are met , If any item does not meet the conditions, it will return to false const result = arr1.every(item => item.state == true) console.log(result); </script>

filter

• Filter the elements in the array that meet the conditions
• arr2.filter(item => item.state == true)

<script> const arr2 = [ {
      id:1 , name:' watermelon ', state:true, price:10, count: 1}, {
      id:2 , name:' durian ', state:false, price:80, count: 2}, {
      id:3 , name:' strawberry ', state:true, price:20, count: 3} ] //  Judge whether the conditions are met , If any item does not meet the conditions, it will return to false let amt = 0; arr2.filter(item => item.state == true).forEach(item => {
       amt += item.price*item.count; }) console.log("amt: ",amt); </script>
			

reduce

• Accumulate each convenient value
• Format ：arr2.reduce(( Cumulative results , Current loop item )=>{return Result after accumulation }, Initial value )

<script> const arr2 = [ {
      id:1 , name:' watermelon ', state:true, price:10, count: 1}, {
      id:2 , name:' durian ', state:false, price:80, count: 2}, {
      id:3 , name:' strawberry ', state:true, price:20, count: 3} ] //  Add up the results of each cycle  // arr2.filter(item => item.state == true).reduce(( Cumulative results , Current loop item )=>{return  Result after accumulation },  Initial value ) const amt1 = arr2.filter(item => item.state == true).reduce((amt,item)=>{
       return amt += item.price*item.count }, 0) //  Another way of writing  // const amt1 = arr2.filter(item => item.state == true).reduce((amt,item)=> amt += item.price*item.count, 0) console.log(amt1); </script>