delay in a for loop for http request

问题:

I am just getting started with JS and Node.js. I am trying to build a simple scraper as first project, using Node.js and some modules such as request and cheerio. I would like to add a 5 secs delay between each http request for each domain contained into the array. Can you explain me how to do it?

Here is my code:

var request = require('request');

var arr = [ "http://allrecipes.com/", "http://www.gossip.fr/" ];

for(var i=0; i < arr.length; i++) {
    request(arr[i], function (error, response, body){
        console.log('error:', error);
        console.log('statusCode:', response && response.statusCode);
        console.log('body:', body);
    });
}

回答1:

Use setTimeout:

var request = require('request');
var arr = ["http://allrecipes.com/", "http://www.gossip.fr/" ];

for (var i = 0; i < arr.length; i++) {
    setTimeout(request, 5000 * i, arr[i], function (error, response, body){
        console.log('error:', error);
        console.log('statusCode:', response && response.statusCode);
        console.log('body:', body);
    });
}

You basically make the loop and say that the request method should be called with a delay equal to 5000 * i, which is 5000ms multiplied by i, so it will increase with 5 seconds for each loop iteration. Then you provide all the arguments that will be passed to the function.