Description: The first line declares a data array and assigns the array content [1,2,3,4,' nas '], then the second line declares the sum variable and assigns the value 0, and the third line uses the data array forEach to execute The function of callback program fragment is introduced, so forEach will start to enumerate the data of the array in array order and execute the callback program fragment. The first value of the array is enumerated 1 for the first time, so the result of sum+=1 is currently sum=1.
The second time enumerates the second value 2 of the array, so the result is sum+=2. Currently, sum=3. The third time the third value is enumerated, the third value 3, so the result is sum+=3. The current sum=6. The fourth time The fourth value 4 of the array is enumerated, so the result of sum+=4 is currently sum=10. The fifth value of the array is new zealand whatsapp phone number enumerated ' nas ', so the result of sum+= ' nas ' is equal to sum=sum+' nas ' , currently sum='10 nas ', the fourth line shows that the current sum value will show '10 nas ', the fifth line uses the data array forEach to execute the function of bringing in the callback program fragment,
so forEach will start to enumerate the array in the order of the array data and execute the callback program fragment. The first value of the array is enumerated 1, so data [0] = 1+1 will be executed. At this time, data[0] will become 2. The second time the array is enumerated. The second value is 2, so data [1] = 2+1 will be executed. At this time, data[1] will become 3. The third value of the array is enumerated for the third time, so data [2] = 3+ will be executed. 1. At this time data[2] will become 4. The fourth value of the array 4 is enumerated for the fourth time, so data [3] = 4+1 will be executed. At this time data[3] will become 5. The fifth time The fifth value of the array ' nas ' is enumerated this time, so data [4] = ' nas '+1 will be executed. At this time, data [4] will become ' nas1 ', and the sixth line outputs the data array result as [2, 3,4,5 ,' nas1 ']