Debug in JavaScript

debugger

In browser, debugger can trigger breakpoint

debugger;

Debug native function

function debug(fn) {
    // Arrow function () => {} cannot be used,
    // Because `this` needs to be bound
    return function () {
        debugger;
        return fn.apply(this, arguments);
    };
}

To debug "string".at()

String.prototype.at = debug(String.prototype.at);

To debug console.log()

console.log = debug(console.log);

Inject function

Inject a function before the target function

function inject(to, fn) {
    return function () {
        fn.apply(this, arguments);
        return to.apply(this, arguments);
    };
}

To log the call stack and arguments when "string".replace() is called

String.prototype.replace = inject(
    String.prototype.replace,
    function () {
        console.trace();
        console.log(arguments);
    }
);

"abc".replace("a", "s");

Call stack trace

Get the call stack

new Error().stack

Print the call stack

console.trace();

console.trace("message");

Debug in node.js

node --inspect server.js