Is the right side of the operator forced to convert to the type on the left?
If a number is equal to a string -> number, is it actually equal to another number?Do both sides get converted to the same underlying type, such as a number?
Can a boolean be equal to a string -> number, and are they truly equivalent?Are there distinct rules for each operator like *-/+||&&% ?
I have reviewed other questions and answers, but find them to be unclear and confusing.
Check out the Abstract Equality Comparison algorithm for the rules.
Do operators force conversion of right side to match type on left?
number == string -> number == number
In Step 4, if Type(x) is Number and Type(y) is String, the result will be x == ToNumber(y).
So, yes.
Are both sides converted to the same underlying type, like number?
boolean == string -> number == number
In Step 6, if Type(x) is Boolean, then the comparison is ToNumber(x) == y.
Since this results in different types (number and string), it goes to Step 4: number == ToNumber(y).
So, yes again.
Do different operators have unique coercion rules such as *-/+||&&%??
Other operators may involve coercion during expression evaluation, so I would say "Yes". Refer to relevant sections of ECMA-262#expressions for more details.
When comparing two different data types in JavaScript (non-strict comparison), the types String, Number, Boolean, or Object are converted as follows:
If you compare a number and a string, the string will be converted to a numerical value. JavaScript tries to convert the alphanumeric characters in the string to a Number type value. It takes the numeric value from the string and rounds it to the nearest Number type value.
When one of the operands is Boolean, the Boolean value true becomes 1, and false becomes +0 during conversion.
For comparisons involving an object with a number or string, JavaScript aims to retrieve the default value for that object. The operators attempt to change the object into a primitive value, either a String or Number value, by utilizing the valueOf and toString methods within the objects.
If converting the object into a primitive value fails, a runtime error occurs. An object is only transformed into a primitive if its counterpart is also a primitive. If both operands are objects, they are compared based on their reference, and the equality test is true only if they refer to the same object.
== ensures that the operands are of the same type before comparing them.
When it comes to relational abstract comparisons (such as <=), both operands are converted to primitives and then to a common type for comparison.
When comparing strings, standard lexicographical ordering is used, based on Unicode values.
For further clarification, refer to the source.
Learn more about abstract equality comparison
Check out JavaScript operator precedence
When comparing values x and y using the '==' operator, the outcome can be either true or false. Here is an overview of how such a comparison happens:
If both x and y are of the same type (Type(x) is equal to Type(y)), then the comparison result will be from performing Strict Equality Comparison x === y.
In cases where one value is null and the other is undefined, the return value is true.
For Number type x and String type y, compare x == ToNumber(y).
For String type x and Number type y, compare Number(x) == y.
When x is Boolean type, compare ToNumber(x) == y.
When y is Boolean type, compare x == ToNumber(y).
If x is String, Number, or Symbol and y is Object, compare x == ToPrimitive(y).
If x is Object and y is String, Number, or Symbol, compare ToPrimitive(x) == y. The final outcome in this case would be false.
Image resources for reference: https://i.sstatic.net/ph1JZ.png https://i.sstatic.net/cjhVw.png https://i.sstatic.net/fpGEi.png https://i.sstatic.net/iYqPN.png https://i.sstatic.net/RnCtk.png https://i.sstatic.net/Pphpw.png
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