Discussion on how php and js transfer data to each other through json

When we combine php and javascript to implement certain functions, json is often used. json is a data format of js and can be parsed directly by js. PHP cannot read json data directly, but PHP provides the json_decode function to convert json data so that it can be accessed by PHP scripts. At the same time, PHP also provides the json_encode function to convert data into json format. So, are the native json in js exactly the same as the json converted by the json_encode function in php? Today, the webmaster will discuss this issue with everyone.

When we pass array data to javascript through php, we usually need to convert it into json format and obtain it through javascript. Let's take the array as an example and first look at the difference between the two.

1. One-dimensional array
Consider PHP array

Copy the code The code is as follows:

$ array=array("1","2","3");

After conversion using the json_encode function, the corresponding json string is

Copy the code and the code is as follows:

["1","2","3"].

Careful friends soon discovered that the json string obtained after conversion is in the form of an array in javascript. So, can it be accessed using the array access method of js?
Of course it is possible, but when you pass this json string to js, you need to use the urlencode function to encode it, such as:

Copy code The code is as follows:

Access json

We can use the following js code to verify:

Copy the code The code is as follows:

 
function show(str){ 
var jobj=eval_r(decodeURI(str)); 
alert(jobj[2]) ; 
} 

If you try it yourself, you will find that yes, you can access it in the same way as accessing a one-dimensional array in js. The eval method interprets the json string as a json object, because what is passed is a string. If it is not converted, you will get the value of the third character in the string.
Let’s make some changes to this one-dimensional array. We found that the one-dimensional array above does not have an index specified, so it defaults to a numeric index. Now let’s add a key name to it:
Consider a php array

Copy code The code is as follows:

$array=array('a'=>'1','b'=> ;'2','c'=>'3');

After conversion using the json_encode function, the corresponding json string is

Copy Code The code is as follows:

{"a":"1","b":"2","c":"3"}

.
We soon discovered the difference. The most obvious one is that the [] at both ends of the string became {}. So can this string be processed as above and accessed by js? Let’s give it a try:

Copy the code The code is as follows:

Access json
function show(str){
var jobj=eval_r(decodeURI(str));
alert(jobj.a);
}

If you try it, you will know that after clicking the link, no pop-up window appears. Why? Is the json string format generated by PHP wrong? No, this is when we used the eval function to explain, an error occurred. Replace the above function code with:

Copy code The code is as follows:

 
function show(str){ 
var jobj=eval_r('('+decodeURI(str)+')'); 
alert(jobj.a); 
} 

Try again! How about it? You can visit now. This tells us that when using the eval method to process a json string with key names, you need to accelerate the brackets at both ends of the string. As for why, the webmaster doesn’t know. He is just standing on the shoulders of giants.
It should be noted here that although the json string
{"a":"1","b":"2","c":"3"} generated by PHP cannot be directly passed to js Interpreted as json format, but if you use this string in js to directly create json data, it is ok. Try the following code:

Copy the code The code is as follows:

 
var jobj={"a":"1","b":"2","c":"3"}; 
alert(jobj.b); 

2. Two-dimensional array
Two-dimensional array is widely used in PHP, so it is very important to understand the json format after the two-dimensional array is converted. With the above example as a basis, the webmaster will directly give the sample code below:

Copy the code The code is as follows:

Access json
function show(str){
var jobj=eval_r(decodeURI(str));
alert(jobj[0][0]);
}

When you run it, you will find that this is similar to a one-dimensional array. This is an example without key names, so in the show function, it is also possible to remove the brackets at both ends of the string.
Next, we make some changes to the two-dimensional array and add key names to the second dimension. Please see the sample code:

Copy the code The code is as follows :

'1',"b"=> '2','3'))));?>')" id="aj">Access json
function show(str){
var jobj=eval_r('( '+decodeURI(str)+')');
alert(jobj[0].a);
}

After everyone ran the code, we found that here we access json data The way is a little different. Above we used
alert(jobj[0][0]);
and here we used
alert(jobj[0].a); Don’t ask me why, that’s it. This is how json is accessed.
In the above example, we added a key name to the second dimension of the two-dimensional array. Next, we add a key name to the first dimension to see what the access methods are different:

Copy code The code is as follows:

Access json
function show(str){
var jobj=eval_r('('+decodeURI(str)+')');
alert(jobj.k[1]);
}

Here we use
jobj.k[1] This way, you must have discovered that as long as the array contains key names, when the array is converted into json format, you must use
json object. Key name
like this method to access the elements under the key. In the above example, the array element under the k key is a numeric index, so use k[1] to access it in json.
Next, we add key names to both the first and second dimensions of the array:

Copy the code The code is as follows:

'1','2','3') )));?>')" id="aj">Access json
function show(str){
var jobj=eval_r('('+decodeURI(str)+' )');
alert(jobj.k.a);
}

As mentioned above, as long as it contains a key name, it must be accessed in the form of
json object.key name
. If there are multiple keys, use
json object.key name. .Key name...
, don’t ask me why, this is how json is accessed. Only the inventor of javascript can explain to you why he stipulated this.
Conclusion:
1. When converting the array in php into a json string and passing it to js. If the array does not specify a key name, you can directly use the eval method of js to convert it into json format for js processing; if the array contains a key name, you need to use
()
when using the eval method to process it. Surround the json string.
2. If the array contains a key name, after converting it into a json string, use the
json object.key name.key name...
method to access it in js. If it is a numerical index Then use
json object [1]
or
json object.key name [1]
.
Above, we mainly discussed the things that need to be paid attention to when passing json string to js in PHP. Next we will discuss how to process the json string when passing it to php using js.
If you are smart, you must already know that as long as the json data is enclosed in quotes and passed to PHP as a string [usually done with ajax], it can be decoded using the json_decode function. That’s right! That's it! But you must be careful when constructing json strings. If you don’t often construct json strings, you might as well use
echo json_encode(array('k'=>array("a"=>'1', '2','3')))
In this way, view the json format of the target string you need to construct. In this way you can construct it in js according to the results you want!
Okay, today we have discussed how to use json data to communicate between php and js. You can try to pass the object type of php to js after json encoding.

Discussion on how php and js transfer data to each other through json_PHP Tutorial