話不多說(shuō)，直接上代碼：

function grade(grade){
    switch(true) {
        case grade>=90: 
            console.log('A'); break;
        case grade>=80: 
            console.log('B'); break;
        case grade>=70: 
            console.log('C'); break;
        case grade>=60: 
            console.log('D'); break;
        default:
            console.log('E'); break;
    }
}