Variables

In Navi Stream we have 3 keywords to store value: let, var and varip.

The syntax of variable declarations is:

[<declaration_mode>] :[<type>] <identifier> = <expression>

where:

• declaration_mode - is the variable mode, we can use let, var, varip 3 kinds.
• type - used to declare the variable type, such as number, string (optional parameter).
• identifier - variable name.
• expression - the value of the variable, can be any expression.

let

let for define a mutable variable. Like let in JavaScript.

INFO

We don't have mutable and inmutable types in Navi Stream, so you can change the value of a variable at any time.

let b = 8;
let a = 1 + b;
// Now `a` value is 9

a += 2;
// Now `a` value is 11

You can assignment a new value to a variable at any time.

let a = 1;
a = 2;
a = 3;

var

var use for stream processing, it's like let but it's reset to the initial value at the end of each period.

TIP

var is a periodic let, its value is only fixed at the end of each period, and other times it is reset to the value at the beginning of the period.

The following example shows how to use var to calculate the current period:

var bar = 0;

bar += 1;

After run the code, we can get the following result:

idx	bar
1	0
2	0
3	0
4	0
5	1
6	1
7	1
8	1
9	1
10	2

The result is consistent with the 5m periodic rule, you can see that the value of var variable is only determined at the end of the last 5m.

The following diagram shows the change of the var variable:

varip

varip use for stream processing, ensure that the value of each period is independent.

Use case

idx	time	price	volume
1	10:00	100.25	300
2	10:01	100.50	200
3	10:02	100.75	100
4	10:03	101.00	300
5	10:04	101.25	200
6	10:05	101.50	100
7	10:06	101.75	300
8	10:07	102.00	200
9	10:08	102.25	100
10	10:09	102.50	300
11	10:10	102.75	200

Now, we use varip to calculate the total amount of each period (5m):

varip total_amount = 0;

total_amount += trade.volume;

If we calculate it, we can get:

idx	total_amount
1	300
2	500
3	600
4	900
5	1100
6	1200
7	1500
8	1700
9	1800
10	2100
11	2300

barstate.is_confirmed

WARNING

Navi Stream's calculation cycle is a little special, the last data in each cycle (period) will be calculated twice, the last data will be calculated once in confirmed mode.

When in the last data of the period, barstate.is_confirmed is true, so we need to judge it to avoid total_amount being calculated twice.

We expected to output data only at the end of each period, so we can write like this:

varip total_amount = 0;

if (barstate.is_confirmed) {
  alert(`total_amount: {total_amount}`);
} else {
  total_amount += trade.volume;
}

Then Navi Stream well send alert like this:

idx	total_amount
5	"total_amount 1100"
11	"total_amount 2300"