1-1 联合类型1-2 类型断言 1-1 联合类型let strOrnum:string |number;/* 联合类型 */ 1-2 类型断言function getLen(params:string | number) :number{ const str = params as string; if(str.length){ return str.length; }else{ const num = params as number; return num.toString().length; }}