JSON – stringify and parse

Converts a JavaScript value into a JSON-formatted string.

Part of: JavaScript Coding without HTML and CSS — Module 46

Understanding JSON – stringify and parse in JavaScript

What it does: This is exactly what the stringify() method does. stringify() turns an object or array into a JSON-formatted string. JavaScript requires all capitals: JSON.stringify(). JavaScript is case-sensitive, so 'stringify' must be lowercase. Both objects and arrays can be converted into JSON strings. The text must be valid JSON, or parse() will throw an error. JavaScript's built-in object is JSON, not json. The method name is parse(), not Parse().

Common mistakes: 'JSON' must be capitalized - it's not 'json'. 'stringify' must be lowercase - a capital S causes an error.

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This module's key terms are also in a printable crossword (Modules 41–52) and word search (Modules 21–52).

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Learning

Duo

Does JSON.stringify() convert a JS value into a JSON string?

YesNo

Matches

let j = json.stringify(obj);

↓

Wrong - 'JSON' must be capitalized

Applying

Meanings

Term

JSON.stringify()

Meaning

Converts a JavaScript value into a JSON-formatted string.

Practice

let person = {name: "Sam", age: 12};

Testing

Gaps

let json = JSON.(person);

Check Answer

Spots

1let j = json.parse(s);

2let s = '{"a":1}';

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Quick Questions

1. Does JSON.stringify() convert a JS value into a JSON string?

A. No

B. Yes ✓

stringify() turns an object or array into a JSON-formatted string.

2. Does JSON.parse() convert a JSON string into a JS value?

A. No

B. Yes ✓

parse() turns a JSON string back into a usable object or value.

3. Is 'json' with a lowercase j valid for JSON.stringify()?

A. No ✓

B. Yes

JavaScript requires all capitals: JSON.stringify().

4. Must 'stringify' be written in lowercase?

A. Yes ✓

B. No

JavaScript is case-sensitive, so 'stringify' must be lowercase.

5. Must 'parse' be written in lowercase?

A. Yes ✓

B. No

JavaScript is case-sensitive, so 'parse' must be lowercase.

Match the Pairs

JSON.stringify(person) → Converts the person object into a JSON string

JSON.parse(json) → Converts a JSON string back into a JS value

Converts a JS value into a JSON-formatted string → JSON.stringify(data)

Converts a JSON string into a usable JS value → JSON.parse(text)

let j = json.stringify(obj); → Wrong - 'JSON' must be capitalized

let o = JSON.Parse(text); → Wrong - 'parse' must be lowercase

Key Term

JSON.stringify()

Converts a JavaScript value into a JSON-formatted string.

Fill in the Blanks

1. let json = JSON.stringify(person);

Hint: Type the method that converts a value into a JSON string.

2. let obj = JSON.parse(json);

Hint: Type the method that converts a JSON string back into a value.

3. let text = JSON.stringify(data);

Hint: Type the method that converts a value into a JSON string.

4. let result = JSON.parse(text);

Hint: Type the method that converts a JSON string back into a value.

5. let data2 = JSON.stringify({a: 1});

Hint: Type the method that converts a value into a JSON string.

Spot the Error

Question 1

A let j = json.parse(s);

B let s = '{"a":1}';

C console.log(j);

Line A — 'JSON' must be capitalized - it's not 'json'.

Question 2

A let t = {b: 2};

B let j = JSON.Stringify(t);

C console.log(j);

Line B — 'stringify' must be lowercase - a capital S causes an error.

Question 3

A let u = {c: 3};

B let j2 = JSON.stringify(u);

C let k = JSON.Parse(j2);

Line C — 'parse' must be lowercase - a capital P causes an error.

Question 4

A let m = Json.stringify(x);

B let x = {d: 4};

C console.log(m);

Line A — 'JSON' must be all uppercase, not 'Json'.

Question 5

A let y = {e: 5};

B let n = JSON.stringfy(y);

C console.log(n);

Line B — 'stringify' is misspelled as 'stringfy'.

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