export default {} // 根据初始值推论 // 相当于 let uname: string = "陈乔恩"; let uname = "陈乔恩"; uname = "徐璐"; // uname = 123; // uname = true; // 相当于 let x: (number | null)[] = [0, 1, null]; let x = [0, 1, null]; // x = [20, 30 , 40, 50, null, "abc", true]; // 这里不能进行类型推论 // let uage; // uage = 123; // uage = true; // 根据上下文推论 window.onmousedown = function(mouseEvent) { mouseEvent.button mouseEvent.clientX }