++[[]][+[]]+[+[]]

Solution:

++[[]][+[]]
+
[+[]]

++[[]][0]
+
[0]

• [[]][0] returns the inner array ([]). Due to references it's wrong to say [[]][0] === [], but let's call the inner array A to avoid the wrong notation.
• ++[[]][0] == A + 1, since ++ means 'increment by one'.
• ++[[]][0] === +(A + 1); in other words, it will always be a number (+1 does not necessarily return a number, whereas ++ always does - thanks to Tim Down for pointing this out).

+([] + 1)
+
[0]

• +([] + 1) === +("" + 1), and
• +("" + 1) === +("1"), and
• +("1") === 1

1
+
[0]

1
+
"0"

=== "10" // Yay!

     11.4.6 Unary + Operator

The unary + operator converts its operand to Number type.

The production UnaryExpression : + UnaryExpression is evaluated as follows:

1. Let expr be the result of evaluating UnaryExpression.
2. Return ToNumber(GetValue(expr)).

       Object

Apply the following steps:

1. Let primValue be ToPrimitive(input argument, hint String).
2. Return ToString(primValue).

         Object

Return a default value for the Object. The default value of an object is retrieved by calling the [[DefaultValue]] internal method of the object, passing the optional hint PreferredType. The behaviour of the [[DefaultValue]] internal method is defined by this specification for all native ECMAScript objects in 8.12.8.

        8.12.8 [[DefaultValue]] (hint)

When the [[DefaultValue]] internal method of O is called with hint String, the following steps are taken:

1. Let toString be the result of calling the [[Get]] internal method of object O with argument "toString".
2. If IsCallable(toString) is true then,

a. Let str be the result of calling the [[Call]] internal method of toString, with O as the this value and an empty argument list.

b. If str is a primitive value, return str.

        15.4.4.2 Array.prototype.toString ( )

When the toString method is called, the following steps are taken:

1. Let array be the result of calling ToObject on the this value.
2. Let func be the result of calling the [[Get]] internal method of array with argument "join".
3. If IsCallable(func) is false, then let func be the standard built-in method Object.prototype.toString (15.2.4.2).
4. Return the result of calling the [[Call]] internal method of func providing array as the this value and an empty arguments list.

       11.4.6 Unary + Operator

The unary + operator converts its operand to Number type.

The production UnaryExpression : + UnaryExpression is evaluated as follows:

1. Let expr be the result of evaluating UnaryExpression.
2. Return ToNumber(GetValue(expr)).

     The MV of StringNumericLiteral ::: [empty] is 0.

$myText = $myVar . '';

Answer:

$myText = (string)$myVar;

var string = "foo",
    substring = "oo";
string.includes(substring);

var string = "foo",
    expr= "/oo/";
string.search(expr);

var string = "foo",
    substring = "oo";
_.includes(string, substring);

var string = "foo",
    expr= "/oo/";
expr.test(string);

var string = "foo",
    expr= "/oo/";
string.match(expr);

var string = "foo",
    substring = "oo";
console.log(string.indexOf(substring) !== -1);