What are the parameters for the number Pipe - Angular 2

From the DOCS

Formats a number as text. Group sizing and separator and other locale-specific configurations are based on the active locale.

SYNTAX:

number_expression | number[:digitInfo[:locale]]

where expression is a number:

digitInfo is a string which has a following format:

{minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}

• minIntegerDigits is the minimum number of integer digits to use.Defaults to 1
• minFractionDigits is the minimum number of digits
• after fraction. Defaults to 0. maxFractionDigits is the maximum number of digits after fraction. Defaults to 3.
• locale is a string defining the locale to use (uses the current LOCALE_ID by default)

DEMO

The parameter has this syntax:

{minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}

So your example of '1.2-2' means:

• A minimum of 1 digit will be shown before decimal point
• It will show at least 2 digits after decimal point
• But not more than 2 digits

1. Regarding your first question.The pipe works as follows:

   numberValue | number: {minIntegerDigits}.{minFractionDigits}-{maxFractionDigits}

   • minIntegerDigits: Minimum number of integer digits to show before decimal point,set to 1by default

   • minFractionDigits: Minimum number of integer digits to show after the decimal point

   • maxFractionDigits: Maximum number of integer digits to show after the decimal point

2.Regarding your second question, Filter to zero decimal places as follows:

{{ numberValue | number: '1.0-0' }}

For further reading, checkout the following blog