Evaluate the Javascript string and save the output

Question

Evaluate the Javascript string and save the output

My challenge involves receiving JavaScript as a string that needs to be executed and compared to a specific output. Currently, I am utilizing the eval() function for this task, but I am open to alternatives. The execution takes place on the client side within a web browser.

Is there a method to accomplish this without modifying the string a?

let a = "console.log(\"a\")";
eval(a);
let stdout = ???

javascript

Answer 1

Answer №1

Utilizing:

bind()
call()

One can enhance console.log to maintain an additional, separate real-time log of all the entries.

In the practical example provided below, each time something is logged to the console, it is also appended to the console.stdout array.

Practical Example:

console.stdout = [];
console.logInclStdout = console.log.bind(console);

console.log = (logEntry) => {
    console.stdout.push(logEntry);
    console.logInclStdout.call(console, logEntry);
}


let a = "console.log('a')";
let b = "console.log('b')";
let c = "console.log('c')";

let saferFasterEval = (input) => Function(`"use strict"; ${input}`)();

saferFasterEval(a);
saferFasterEval(b);
saferFasterEval(c);

// To view the logs made via console.log
console.info(console.stdout);

Answer 2

Utilizing:

bind()
call()

One can enhance console.log to maintain an additional, separate real-time log of all the entries.

In the practical example provided below, each time something is logged to the console, it is also appended to the console.stdout array.

Practical Example:

console.stdout = [];
console.logInclStdout = console.log.bind(console);

console.log = (logEntry) => {
    console.stdout.push(logEntry);
    console.logInclStdout.call(console, logEntry);
}


let a = "console.log('a')";
let b = "console.log('b')";
let c = "console.log('c')";

let saferFasterEval = (input) => Function(`"use strict"; ${input}`)();

saferFasterEval(a);
saferFasterEval(b);
saferFasterEval(c);

// To view the logs made via console.log
console.info(console.stdout);

Answer 3

Answer №2

To preserve the messages outputted through console.log within the eval function, one approach could involve replacing the console.log function. However, it is generally advised against this practice and using eval altogether.

// Save the original console.log function
const original = console.log;

// Initialize an array to store the commands
const commands = [];

// Override console.log to capture the logs
console.log = (msg) => { commands.push(msg) };

// Execute operation A
let a = "console.log(\"a\")";
eval(a);

// Execute operation B
let b = "console.log(\"b\")";
eval(b);

// Execute operation C
let c = "console.log(\"c\")";
eval(c);

// Retrieve the log messages; Convert them to a string using `commands.join('\n')`
let output = commands;

// Restore the original console.log
console.log = original

Sample: https://jsfiddle.net/x0w2q4Le/4/

Answer 4

To preserve the messages outputted through console.log within the eval function, one approach could involve replacing the console.log function. However, it is generally advised against this practice and using eval altogether.

// Save the original console.log function
const original = console.log;

// Initialize an array to store the commands
const commands = [];

// Override console.log to capture the logs
console.log = (msg) => { commands.push(msg) };

// Execute operation A
let a = "console.log(\"a\")";
eval(a);

// Execute operation B
let b = "console.log(\"b\")";
eval(b);

// Execute operation C
let c = "console.log(\"c\")";
eval(c);

// Retrieve the log messages; Convert them to a string using `commands.join('\n')`
let output = commands;

// Restore the original console.log
console.log = original

Sample: https://jsfiddle.net/x0w2q4Le/4/

Answer 5

Answer №3

When using eval function, the output can be stored in a variable like this:

let x = `
    let num = 5
    num += 2
    num
`
let result = eval(x)

Ensure to place the value you intend to return at the end

Answer 6

When using eval function, the output can be stored in a variable like this:

let x = `
    let num = 5
    num += 2
    num
`
let result = eval(x)

Ensure to place the value you intend to return at the end

Evaluate the Javascript string and save the output

Answer №1

Answer №2

Answer №3

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