Javascript json null value

JSON.parse()

The JSON.parse() static method parses a JSON string, constructing the JavaScript value or object described by the string. An optional reviver function can be provided to perform a transformation on the resulting object before it is returned.

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Syntax

JSON.parse(text) JSON.parse(text, reviver) 

Parameters

The string to parse as JSON. See the JSON object for a description of JSON syntax.

If a function, this prescribes how each value originally produced by parsing is transformed before being returned. Non-callable values are ignored. The function is called with the following arguments:

The key associated with the value.

The value produced by parsing.

Return value

The Object , Array , string, number, boolean, or null value corresponding to the given JSON text .

Exceptions

Thrown if the string to parse is not valid JSON.

Description

JSON.parse() parses a JSON string according to the JSON grammar, then evaluates the string as if it’s a JavaScript expression. The only instance where a piece of JSON text represents a different value from the same JavaScript expression is when dealing with the «__proto__» key — see Object literal syntax vs. JSON.

The reviver parameter

If a reviver is specified, the value computed by parsing is transformed before being returned. Specifically, the computed value and all its properties (in a depth-first fashion, beginning with the most nested properties and proceeding to the original value itself) are individually run through the reviver .

The reviver is called with the object containing the property being processed as this , and two arguments: key and value , representing the property name as a string (even for arrays) and the property value. If the reviver function returns undefined (or returns no value — for example, if execution falls off the end of the function), the property is deleted from the object. Otherwise, the property is redefined to be the return value. If the reviver only transforms some values and not others, be certain to return all untransformed values as-is — otherwise, they will be deleted from the resulting object.

Similar to the replacer parameter of JSON.stringify() , reviver will be last called on the root object with an empty string as the key and the root object as the value . For JSON text parsing to primitive values, reviver will be called once.

Note that reviver is run after the value is parsed. So, for example, numbers in JSON text will have already been converted to JavaScript numbers, and may lose precision in the process. To transfer large numbers without loss of precision, serialize them as strings, and revive them to BigInts, or other appropriate arbitrary precision formats.

Examples

Using JSON.parse()

JSON.parse("<>"); // <> JSON.parse("true"); // true JSON.parse('"foo"'); // "foo" JSON.parse('[1, 5, "false"]'); // [1, 5, "false"] JSON.parse("null"); // null 

Using the reviver parameter

JSON.parse( '', (key, value) => typeof value === "number" ? value * 2 // return value * 2 for numbers : value, // return everything else unchanged ); // JSON.parse('>>', (key, value) =>  console.log(key); return value; >); // 1 // 2 // 4 // 6 // 5 // 3 // "" 

Using reviver when paired with the replacer of JSON.stringify()

In order for a value to properly round-trip (that is, it gets deserialized to the same original object), the serialization process must preserve the type information. For example, you can use the replacer parameter of JSON.stringify() for this purpose:

// Maps are normally serialized as objects with no properties. // We can use the replacer to specify the entries to be serialized. const map = new Map([ [1, "one"], [2, "two"], [3, "three"], ]); const jsonText = JSON.stringify(map, (key, value) => value instanceof Map ? Array.from(value.entries()) : value, ); console.log(jsonText); // [[1,"one"],[2,"two"],[3,"three"]] const map2 = JSON.parse(jsonText, (key, value) => key === "" ? new Map(value) : value, ); console.log(map2); // Map < 1 =>"one", 2 => "two", 3 => "three" > 

Because JSON has no syntax space for annotating type metadata, in order to revive values that are not plain objects, you have to consider one of the following:

• Serialize the entire object to a string and prefix it with a type tag.
• «Guess» based on the structure of the data (for example, an array of two-member arrays)
• If the shape of the payload is fixed, based on the property name (for example, all properties called registry hold Map objects).

JSON.parse() does not allow trailing commas

// both will throw a SyntaxError JSON.parse("[1, 2, 3, 4, ]"); JSON.parse(''); 

JSON.parse() does not allow single quotes

// will throw a SyntaxError JSON.parse(""); 

Specifications

Browser compatibility

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See also

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how to check null value in json object in javascript?

To check the null value in a JSON object in javascript, Just use the if statement or ternary operator before using the JSON object value. it will handle all falsy values with null.

JavaScript if statement or ternary opertor will handle («») , null , undefined , false and the numbers 0 and NaN .

Let’s take a short example check the null value in JSON object in javascript.

// Using if statement  if(obj.value)  console.log("Value have data") > else   console.log("Value is null or falsy value") >  // ternary opertor  obj.value ? "Value have data" : "Value is null or falsy value" ; 

Or if want to check only null values in a JSON object, you can compare your object value with the null datatype. like the below example.

if(obj.value == null)  console.log("Value is null") > else   console.log("Value is not null") > 

Today, I’m going to show you How do I check the null value in JSON object in javascript, as above mentioned, I’m going to use if statement or ternary operator to validate object value is null or not.

Let’s start today’s tutorial how do you check the null value in JSON object in javascript?

Let’s create a sample object with null data and apply all the above-mentioned methods to it.

Check null using the if statement#

To check null in if statement directly mention key in if statement it will go inside else method if object value contains any false value.

let obj =   name: null >  if(obj.name)  console.log("name have data") > else   console.log("name is null") >  // output: "name is null" 

Check null ternary opertor#

To check null in ternary opertor mention object key in the ternary statement if key contains null it will print name is null .

let obj =   name: null >  obj.name ? "name have data" : "name is null" ;  // Output // name is null 

Check only null in a JSON object#

To check only the null value in a JSON object, we will compare it with the null in the if statement. if the value is null it will print a null value.

let obj =   name: null >  if(obj.name == null)  console.log("name is null") > else   console.log("name is not null") >  // Output // name is null 

I hope it helps you, All the best 👍.

Источник

how to check null value in json object in javascript?

To check the null value in a JSON object in javascript, Just use the if statement or ternary operator before using the JSON object value. it will handle all falsy values with null.

JavaScript if statement or ternary opertor will handle («») , null , undefined , false and the numbers 0 and NaN .

Let’s take a short example check the null value in JSON object in javascript.

// Using if statement  if(obj.value)  console.log("Value have data") > else   console.log("Value is null or falsy value") >  // ternary opertor  obj.value ? "Value have data" : "Value is null or falsy value" ; 

Or if want to check only null values in a JSON object, you can compare your object value with the null datatype. like the below example.

if(obj.value == null)  console.log("Value is null") > else   console.log("Value is not null") > 

Today, I’m going to show you How do I check the null value in JSON object in javascript, as above mentioned, I’m going to use if statement or ternary operator to validate object value is null or not.

Let’s start today’s tutorial how do you check the null value in JSON object in javascript?

Let’s create a sample object with null data and apply all the above-mentioned methods to it.

Check null using the if statement#

To check null in if statement directly mention key in if statement it will go inside else method if object value contains any false value.

let obj =   name: null >  if(obj.name)  console.log("name have data") > else   console.log("name is null") >  // output: "name is null" 

Check null ternary opertor#

To check null in ternary opertor mention object key in the ternary statement if key contains null it will print name is null .

let obj =   name: null >  obj.name ? "name have data" : "name is null" ;  // Output // name is null 

Check only null in a JSON object#

To check only the null value in a JSON object, we will compare it with the null in the if statement. if the value is null it will print a null value.

let obj =   name: null >  if(obj.name == null)  console.log("name is null") > else   console.log("name is not null") >  // Output // name is null 

I hope it helps you, All the best 👍.

Источник

JSON Data Types

In JSON, values must be one of the following data types:

• a string
• a number
• an object (JSON object)
• an array
• a boolean
• null

JSON values cannot be one of the following data types:

JSON Strings

Strings in JSON must be written in double quotes.

Example

JSON Numbers

Numbers in JSON must be an integer or a floating point.

Example

JSON Objects

Values in JSON can be objects.

Example

Objects as values in JSON must follow the JSON syntax.

JSON Arrays

Values in JSON can be arrays.

Example

JSON Booleans

Values in JSON can be true/false.

Example

JSON null

Values in JSON can be null.

Example

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