Javascript：如何从断点数组呈现以前的断点

Question

Javascript：如何从媒体类型数组呈现先前的断点。function getCurrentBreakpoint(mediaType) {  const mediaTypes = ["xs", "sm", "md", "lg", "xl", "infinity"];  //suppose current mediaType is `infinity`   // I have to return mediaType as `xl` . always one prevoius state from the current.}目前可以通过使用来实现if ... else or by switch case let breakpoint;  switch (mediaType) {    case "infinity":      breakpoint = "xl";      break;    case "xl":      breakpoint = "lg";      break;    case "lg":      breakpoint = "md";      break;    case "md":      breakpoint = "sm";      break;    default:      breakpoint = "xs";  }

Answer 1

您可以使用Array.prototype.indexOf()如下方式返回相对于传入参数的前一个元素：

function getCurrentBreakpoint(mediaType) {

  const mediaTypes = ["xs", "sm", "md", "lg", "xl", "infinity"];

  let i = mediaTypes.indexOf(mediaType);

  return mediaTypes[i - (i == 0 ? 0 : 1)];

}

console.log(getCurrentBreakpoint('infinity'));

console.log(getCurrentBreakpoint('sm'));

console.log(getCurrentBreakpoint('xs'));