萌新！js 更改箭头函数写法就报错？

Question

functionunique(arr){
returnarr.reduce((prev,cur)=>prev.includes(cur)?prev:[...prev,cur],[]);
}
vararr=[1,1,'true','true',true,true,15,15,false,false,undefined,undefined,null,null,NaN,NaN,'NaN',0,0,'a','a',{},{}];
console.log(unique(arr));
//正常打印
functionunique(arr){
returnarr.reduce((prev,cur)=>{
returnprev.includes(cur)?prev:[...prev,cur],[];
});
}
vararr=[1,1,'true','true',true,true,15,15,false,false,undefined,undefined,null,null,NaN,NaN,'NaN',0,0,'a','a',{},{}];
console.log(unique(arr));
//错报
问题描述
更改了箭头函数的写法为什么就会报错？
UncaughtTypeError:prev.includesisnotafunction

Answer 1

reduce的第二个参数没传functionunique(arr){returnarr.reduce((prev,cur)=>{returnprev.includes(cur)?prev:[...prev,cur];},[]);}vararr=[1,1,'true','true',true,true,15,15,false,false,undefined,undefined,null,null,NaN,NaN,'NaN',0,0,'a','a',{},{}];console.log(unique(arr));

Answer 2

functionunique(arr){returnarr.reduce((prev,cur)=>{returnprev.includes(cur)?prev:[...prev,cur];},[]);}vararr=[1,1,'true','true',true,true,15,15,false,false,undefined,undefined,null,null,NaN,NaN,'NaN',0,0,'a','a',{},{}];console.log(unique(arr));