function onLine(callback){
    var img = new Image();
    img.src = '/assets/img/img1.26736430.png';
    img.onload=function(){
        if (callback) callback(true)        
    };
    img.onerror=function(){
        if (callback) callback(false)
    };
}  
onLine(function(flag){
    if(flag){
        console.log('网络畅通')
    }else{
        console.log('网络故障')
    }
})