如何根据变量的值为url设置正确的条件？ （JavaScript的）

Question

My script javascript like this :

<script>

    var url = 'http://my-app.test/item';
    var sessionBrand = 'honda';
    var sessionModel = 'jazz';
    var sessionCategory = 'velg';
    var sessionKeyword = 'RS 175/60 R 15';

    if(sessionBrand)
        var brand = '?brand='+sessionBrand;
    else
        var brand = '';

    if(sessionModel)
        var model = '&model='+sessionModel;
    else
        var model = '';

    if(sessionCategory)
        var category = '&category='+sessionCategory;
    else
        var category = '';

    if(sessionKeyword)
        var keyword = '&keyword='+this.sessionKeyword;
    else
        var keyword = '';

    var newUrl = url+brand+model+category+keyword;
    console.log(newUrl);

</script>

The result of console.log like this :

http://my-app.test/item?brand=honda&model=jazz&category=velg&keyword=RS 175/60 R 15

var sessionBrand, sessionModel, sessionCategory and sessionKeyword is dynamic. It can change. It can be null or it can have value

I have a problem

For example the case like this :

    var sessionBrand = '';
    var sessionModel = '';
    var sessionCategory = '';
    var sessionKeyword = 'RS 175/60 R 15';

The url to be like this :

http://my-app.test/item&keyword=RS 175/60 R 15

Should the url like this :

http://my-app.test/item?keyword=RS 175/60 R 15

I'm still confused to make the condition

How can I solve this problem?

Answer 1

Just use the array for params and then join them with & separator. For example:

var url = 'http://my-app.test/item';
var sessionBrand = 'honda';
var sessionModel = 'jazz';
var sessionCategory = 'velg';
var sessionKeyword = 'RS 175/60 R 15';

var params = [];

if (sessionBrand) {
    params.push('brand=' + sessionBrand);
}

if (sessionModel) {
    params.push('model=' + sessionModel);
}

if(sessionCategory) {
    params.push('category=' + sessionCategory);
}

if(sessionKeyword) {
    params.push('category=' + sessionCategory);
}
var newUrl = url + '?' + params.join('&');
console.log(newUrl);

Answer 2

The problem with your code is that it is prefacing all query parameters with a & - except for the sessionBrand . What you need in a URL is for the first parameter to start with a ? , and all others with a & . As you saw, your code doesn't do this when there is no sessionBrand .

There are number of ways to fix this. Probably the neatest I can think of is to assemble the various parts as you are, but without any prefixes - then join them all together at the end. Like this (I just saw Viktor's solution, it's exactly the same idea, but neater because he rewrote more of your earlier code):

if(sessionBrand)
    var brand = 'brand='+sessionBrand;
else
    var brand = '';

if(sessionModel)
    var model = 'model='+sessionModel;
else
    var model = '';

if(sessionCategory)
    var category = 'category='+sessionCategory;
else
    var category = '';

if(sessionKeyword)
    var keyword = 'keyword='+this.sessionKeyword;
else
    var keyword = '';

var queryString = '?' + [sessionBrand, sessionModel, sessionCategory, sessionKeyword].filter(function(str) {
    return str.length > 0;
}).join("&");

var newUrl = url+queryString;