JAVASCRIPT

=+ javascript

let a = 2;
let b = 'hello';

console.log(a += 3); // addition
// expected output: 5

console.log(b += ' world'); // concatenation
// expected output: "hello world"

+ javascript

// JavaScript Unary Operators The unary plus operator (+)
// The unary plus ( + ) precedes its operand and evaluates to its operand. It attempts to convert the operand to a number, if it isn't already.

+42           // 42
+"42"         // 42
+true         // 1
+false        // 0
+null         // 0
+undefined    // NaN
+NaN          // NaN
+"foo"        // NaN
+{}           // NaN
+function(){} // NaN

// Note that attempting to convert an array can result in unexpected return values.
// In the background, arrays are first converted to their string representations:

[].toString() === '';
[5].toString() === '5';
[1, 2].toString() === '1,2';

// The operator then attempts to convert those strings to numbers:

+[]           // 0   ( === +'' )
+[5]          // 5   ( === +'5' )
+[1, 2]       // NaN ( === +'1,2' )