Can you explain why the following code doesn't generate any output?
console.log(JSON.stringify(function(){console.log('foobar');}));
Can you explain why the following code doesn't generate any output?
console.log(JSON.stringify(function(){console.log('foobar');}));
When it comes to JSON, functions are unable to be stringified and are handled similarly to undefined or null values. The specific algorithm can be found in EcmaScript 5.1 §15.12.3, with additional information available in the MDN documentation.
Nevertheless, function expressions can still be stringified by converting them into a string representation. For example:
console.log("" + function(){console.log('foobar');})
Converting yourFunctionName to a string using the .toString() method will also stringify the function.One limitation of JSON is its inability to represent functions. This data format was intentionally created for simplicity and universal compatibility among different programming languages, making the inclusion of functions impractical due to lack of cross-language support.
According to the documentation for JSON.stringify:
When converting data to JSON, any undefined values, functions, or XML values will be either omitted (if found in an object) or replaced with null (if found in an array).
If you need to utilize JSON.stringify in a way that also converts functions and native objects, consider passing a converter function as the second argument:
const info = {
myFunc: function(){}
}
function customConverter(key, value) {
if (typeof value === 'function' || value && value.constructor === RegExp) {
return String(value)
}
return value
}
console.log(JSON.stringify(info, customConverter, 4))
If you want to exclude a result, have the converter function return undefined.
The optional third parameter controls the number of spaces for indentation in the output.
Unfortunately, it is not possible to achieve that directly. However, you can utilize third-party libraries for assistance, such as the one found at: https://www.npmjs.com/package/json-fn
There are several techniques for accomplishing this task.
Assume you have a function called bar
> function (bar) { return bar}
If you log it to the console, you will see the function's name and type displayed
> console.log(bar)
[Function: bar]
When you want to access the string version of it, you can use one of the methods below.
> console.log(`${bar}`)
function (baz) { return baz}
undefined
> console.log(bar.toString())
function (baz) { return baz}
undefined
> console.log(""" + bar)
function (baz) { return baz}
undefined
There are a couple of methods to achieve this task. One option is using String(function) and then applying eval() on the result. Another approach involves executing the function code directly through regex, as demonstrated below:
String(function).replace(/\w+\s{1}\w+\(\)\s?\{(\n\s+)?|\(\)\s?=>\s?{(\n\s+)?/, '').replace(/\n?\}/, '')
When utilizing the regex method with eval(), the code within the function will be executed. Make sure to replace "function" in both examples with the name of your function, without the parenthesis at the end.
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