what 's a problem in "Words Order"

output Error: 18,13: Property 'is_checking' does not exist on type 'Global'.

Why???

function wordsOrder(a, b) {
let ar = []
for (let i of a.split(' ')){
    for (let j of b){
        if (i == j){
            ar.push(i)
            break
        }
    }
}
return b.every((e,i)=> e == ar[i])

}

I checked on various browsers - the solution is working! Why does it not work in your application ???