按下按钮时的开关语句不起作用

Question

I want to execute a alert within a switch statement when I´m pressing a button, but it is not working. Even when I´m just having a alert in the prev function, there's no output on my website.

Why?

 var services_array = []; services_array[0] = slider_1; services_array[1] = slider_2; services_array[2] = slider_3; function prev() { alert("prev"); var count = 0; switch (count) { case 0: // 0 = slider_1 // goto slider_3; count = 2; alert(services_array[count]); break; case 1: // 1 = slider_2 // goto slider_1; count--; break; case 2: // 2 = slider_3 // goto slider_2; count--; break; } }

 <button id="btn_backward_service" onclick="prev()"><</button>

Answer 1

You had not defined slider_1 , slider_2 and slider_3 . And every time the code go through your switch block then it assign 2 to count hence every time it will go to services_array[2] and it'll then break out the switch .

 var services_array = []; services_array[0] = 'slider_1'; services_array[1] = 'slider_2'; services_array[2] = 'slider_3'; function prev() { alert("prev"); var count = 0; switch(count) { case 0: // 0 = slider_1 // goto slider_1; count = 0 && alert(services_array[count]); count++; break; case 1: // 1 = slider_2 // goto slider_2; count = 1 && alert(services_array[count]); count++; break; case 2: // 2 = slider_3 count = 3 && alert(services_array[count]); count++; break; } }

 <button id="btn_backward_service" onclick="prev()"> < </button>